Method of terminal transmitting sounding reference signal on the basis of aperiodic sounding reference signal triggering and method for controlling uplink transmission power to transmit aperiodic sounding reference signal

ABSTRACT

The method of the terminal transmitting the SRS on the basis of the aperiodic SRS triggering according to the present invention comprises the steps of: receiving a plurality of aperiodic SRS configuration information from the base station; receiving an aperiodic SRS transmission triggering indicator from the base station; selecting the specific aperiodic SRS configuration information among the plurality of aperiodic SRS configuration information on the basis of at least one among a sub-frame index for receiving the aperiodic SRS transmission triggering indicator, a time relation between the aperiodic SRS transmission sub-frames, and an uplink channel state; and transmitting an aperiodic SRS for the aperiodic SRS transmission triggering indicator on the basis of the selected aperiodic SRS configuration information, the plurality of aperiodic SRS configuration information including the information about a resource for transmitting the aperiodic SRS corresponding to the aperiodic SRS transmission triggering indicator. In addition, according to the present invention, the terminal can be used for receiving a power offset value for transmitting the aperiodic SRS from the base station and determining a transmission power value for transmitting the aperiodic SRS.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2011/004088, filed on Jun. 3, 2011,which claims the benefit of earlier filing date and right of priority toKorean Patent Application No. 10-2011-0053911, filed on Jun. 3, 2011,and also claims the benefit of U.S. Provisional Application Ser. No.61/351,306, filed on Jun. 4, 2010, U.S. Provisional Application Ser. No.61/353,178, filed on Jun. 9, 2010, and U.S. Provisional Application Ser.No. 61/369,654, filed on Jul. 30, 2010, the contents of which are allhereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method for a User Equipment (UE) to transmit aSounding Reference Signal (SRS) based on aperiodic SRS triggering and amethod for a UE to control uplink transmission power for aperiodic SRStransmission.

BACKGROUND ART

Although wireless communication technologies have been developed up toLTE based on Wideband Code Division Multiple Access (WCDMA), demands andexpectation of users and service providers are still on the rise. Sincethe development of other wireless access technologies is in progress,new technology evolution is needed to achieve future competitiveness.Such new technologies require a reduction in cost per bit, an increasein service availability, flexible use of frequency bands, simplestructured and open interfaces, and appropriate power consumption ofUEs.

Recently, standardization of the successor to LTE is in progress in3GPP. In this specification, the successor will be referred to as“LTE-Advanced” or “LTE-A”. Differences of the LTE-A system from the LTEsystem include system bandwidth and introduction of a repeater. TheLTE-A system aims to support a wideband of up to 100 MHz. The LTE-Asystem uses carrier aggregation or bandwidth aggregation technology toachieve a wideband using a plurality of frequency blocks. In the carrieraggregation technology, a plurality of frequency blocks is used as onelarge logic frequency band in order to use a wider frequency band. Thebandwidth of each frequency block may be defined based on the bandwidthof a system block used in the LTE system. Each frequency block istransmitted using a component carrier.

In order to guarantee accurate uplink channel estimation, the 3GPP-LTE-Asystem supports aperiodic SRS transmission in addition to conventionalperiodic SRS transmission. Aperiodic SRS configuration information anduplink transmission power control for aperiodic SRS transmission areneeded to support such aperiodic SRS transmission. However, detailedaperiodic SRS configuration information and methods for controllinguplink transmission power for aperiodic SRS transmission have not yetbeen suggested.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method for a UserEquipment (UE) to transmit a Sounding Reference Signal (SRS) based onaperiodic SRS triggering.

Another object of the present invention is to provide a method for a UEto control uplink transmission power for aperiodic SRS transmission.

Another object of the present invention is to provide a UE fortransmitting an aperiodic SRS based on aperiodic SRS triggering.

Another object of the present invention is to provide a UE forcontrolling uplink transmission power for aperiodic SRS transmission.

Objects of the present invention are not limited to those describedabove and other objects will be clearly understood by those skilled inthe art from the following description.

Technical Solution

A method for transmitting a Sounding Reference Signal (SRS) triggeringbased aperiodic SRS triggering at a user equipment (UE) in a wirelesscommunication system according to the present invention for achievingthe objects may include receiving a plurality of aperiodic SRSconfiguration information from an eNodeB, receiving an aperiodic SRStransmission triggering indicator from the eNodeB, selecting specificaperiodic SRS configuration information from among a plurality ofaperiodic SRS configuration information based on at least one of anindex of a subframe in which the aperiodic SRS transmission triggeringindicator is received, a time relationship between a subframe in whichthe aperiodic SRS transmission triggering indicator is received and acorresponding aperiodic SRS transmission subframe, an uplink channelstate, and transmitting an aperiodic SRS associated with the aperiodicSRS transmission triggering indicator based on the selected aperiodicSRS configuration information, wherein the plurality of aperiodic SRSconfiguration information includes information regarding a resource fortransmitting an aperiodic SRS in response to the aperiodic SRStransmission triggering indicator. Here, the aperiodic SRS may betransmitted through a first aperiodic SRS transmission subframe which isan earliest subframe among the preconfigured periodic SRS transmissionsubframes subsequent to subframe n when the aperiodic SRS transmissiontriggering indicator is received in the subframe n or may be transmittedthrough a second aperiodic SRS transmission subframe which is anearliest subframe among the preconfigured periodic SRS transmissionsubframes subsequent to subframe n+3 when the aperiodic SRS transmissiontriggering indicator is received in the subframe n.

When the index n of the subframe in which the aperiodic SRS transmissiontriggering indicator is received is even, the aperiodic SRS transmissionmay include transmitting the aperiodic SRS through a partial band in afrequency axis of the first aperiodic SRS subframe or the secondaperiodic SRS subframe. Here, when transmission power for transmittingthe aperiodic SRS corresponding to the aperiodic SRS transmissiontriggering indicator is not sufficient, the aperiodic SRS may betransmitted through a fallback aperiodic SRS resource predefined in thepartial band.

On the other hand, when the index n of the subframe in which theaperiodic SRS transmission triggering indicator is received is odd, theaperiodic SRS transmission may include transmitting the aperiodic SRSthrough a full band in a frequency axis of the first aperiodic SRSsubframe or the second aperiodic SRS subframe. Here, when transmissionpower for transmitting the aperiodic SRS corresponding to the aperiodicSRS transmission triggering indicator is not sufficient, the aperiodicSRS may be transmitted through a fallback aperiodic SRS resourcepredefined in the full band.

In addition, when a time difference between the subframe n in which theaperiodic SRS transmission triggering indicator is received and at leastone periodic SRS transmission subframe allocated to the UE correspondsto 4 subframes, a first periodic SRS configuration may be selected fromthe plurality of aperiodic SRS configurations and the aperiodic SRS maybe transmitted through the first aperiodic SRS subframe according to thefirst aperiodic SRS configuration. Here, the aperiodic SRS may betransmitted through a full band in a frequency axis of the firstaperiodic SRS subframe.

On the other hand, when a time difference between the subframe n inwhich the aperiodic SRS transmission triggering indicator is receivedand at least one periodic SRS transmission subframe allocated to the UEdoes not correspond to 4 subframes, a second periodic SRS configurationis selected from the plurality of aperiodic SRS configurations and theaperiodic SRS is transmitted through the second aperiodic SRS subframeaccording to the second aperiodic SRS configuration. Here, the aperiodicSRS may be transmitted through a partial band in a frequency axis of thesecond aperiodic SRS subframe.

When the uplink channel state is worse than a predefined channel state,a second aperiodic SRS configuration may be selected from the pluralityof aperiodic SRS configurations and the aperiodic SRS may be transmittedthrough a partial band in a frequency axis of the second aperiodic SRSsubframe or the first aperiodic SRS subframe according to the secondaperiodic SRS configuration.

On the other hand, when the uplink channel state is better than apredefined channel state, a second aperiodic SRS configuration may beselected from the plurality of aperiodic SRS configurations and theaperiodic SRS may be transmitted through a full band in a frequency axisof the second aperiodic SRS subframe or the first aperiodic SRS subframeaccording to the first aperiodic SRS configuration.

A method for controlling an uplink transmission power for aperiodicSounding Reference Signal (SRS) transmission at a user equipment (UE) ina wireless communication system according to an embodiment of thepresent invention for achieving the objects may include receiving apower offset value for the aperiodic SRS transmission from an eNodeB,determining an aperiodic SRS transmission power value using the poweroffset value for the aperiodic SRS transmission, and transmitting anaperiodic SRS using the determined aperiodic SRS transmission powervalue. The power offset value only for the aperiodic SRS transmissionmay be a UE-specific value received through higher layer signaling. Inaddition, the method may further include receiving the aperiodic SRStransmission triggering indicator from the eNodeB, wherein the aperiodicSRS transmission may be performed according to the aperiodic SRStransmission triggering indicator.

A method for controlling an uplink transmission power for aperiodicSounding Reference Signal (SRS) transmission at a User Equipment (UE) ina wireless communication system according to another embodiment of thepresent invention for achieving the objects may include receiving apower offset value for periodic SRS transmission and a power offsetvalue for aperiodic SRS transmission from an eNodeB, receiving anindicator for triggering aperiodic SRS transmission from the eNodeB, anddetermining a transmission power value for the aperiodic SRStransmission using the power offset value for the aperiodic SRStransmission according to the aperiodic SRS transmission triggeringindicator.

A user equipment for transmitting a Sounding Reference Signal (SRS)based on aperiodic SRS triggering for achieving the objects may includea receiver configured to receive a plurality of aperiodic SRSconfiguration information and an aperiodic SRS transmission triggeringindicator from an eNodeB, a processor configured to select specificaperiodic SRS configuration information from among a plurality ofaperiodic SRS configuration information based on at least one of anindex of a subframe in which the aperiodic SRS transmission triggeringindicator is received, a time relationship between a subframe in whichthe aperiodic SRS transmission triggering indicator is received and acorresponding aperiodic SRS transmission subframe, an uplink channelstate, and a transmitter configured to transmit an aperiodic SRSassociated with the aperiodic SRS transmission triggering indicatorbased on the selected aperiodic SRS configuration information, whereinthe plurality of aperiodic SRS configuration information may includeinformation regarding resources for transmitting an aperiodic SRS inresponse to the aperiodic SRS transmission triggering indicator.

A user equipment for controlling uplink transmission power for aperiodicSounding Reference Signal (SRS) transmission in a wireless communicationsystem according to the present invention for the objects may include areceiver configured to receive a power offset value for the aperiodicSRS transmission from an eNodeB, a processor configured to determine anaperiodic SRS transmission power value using the power offset value forthe aperiodic SRS transmission, and a transmitter configured to transmitan aperiodic SRS using the determined aperiodic SRS transmission powervalue.

Advantageous Effects

The UE transmits aperiodic SRSs according to an aperiodic SRSconfiguration according to the present invention, thereby enabling morecorrect uplink channel state estimation. In addition, the UE selectsspecific aperiodic SRS configuration information from among a pluralityof aperiodic SRS configuration information based on at least one of anindex of a subframe in which the aperiodic SRS transmission triggeringindicator is received, a time relationship between a subframe in whichthe aperiodic SRS transmission triggering indicator is received and acorresponding aperiodic SRS transmission subframe, an uplink channelstate, thereby improving communication performance.

In addition, the method not only contributes to more correctlyestimating the uplink channel state but can also efficiently overcome anSRS coverage problem and an uplink signal interference problem in aco-channel HetNet of the same channel through adaptive aperiodic SRSconfiguration switching.

Further, it is possible to determine an aperiodic SRS transmission powerusing an uplink power control equation for aperiodic SRS transmissionsuggested in the present invention and to transmit an aperiodic SRSusing the determined power.

Advantages of the present invention are not limited to those describedabove and other advantages will be clearly understood by those skilledin the art from the following description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a block diagram illustrating a configuration of an eNodeB anda UE in a wireless communication system according to the presentinvention.

FIG. 2 illustrates a structure of a radio frame used in a 3GPP LTEsystem which is an exemplary mobile communication system.

FIGS. 3A and 3B illustrate structures of downlink and uplink subframesin a 3GPP LTE system which is an exemplary mobile communication system.

FIG. 4 illustrates a downlink time-frequency resource grid structureused in the present invention.

FIG. 5 illustrates a configuration of a general MIMO communicationsystem.

FIG. 6 illustrates channels from N_(T) transmit antennas to receiveantenna i.

FIGS. 7(a) and 7(b) illustrate a reference signal pattern in a 3GPP LTEsystem which is an exemplary mobile communication system, where FIG.7(a) illustrates a reference signal pattern when a normal Cyclic Prefix(CP) is applied and FIG. 7(b) illustrates a reference signal patternwhen an extended CP is applied.

FIG. 8 illustrates an exemplary uplink subframe configuration includingan SRS symbol.

FIGS. 9A and 9B illustrate an exemplary subframe for cell-specificperiodic SRS transmission and an exemplary subframe for UE-specificperiodic SRS transmission.

FIGS. 10A, 10B, and 10C illustrate exemplary operations for adaptivelyselecting multiple SRS configurations using a time relationship betweena subframe in which an aperiodic SRS triggering grant is received and asubframe in which a corresponding aperiodic SRS is transmitted.

FIG. 11 illustrates an aperiodic SRS operation performed whenclassification of the index of a subframe corresponding to the timepoint at which an aperiodic SRS triggering grant arrives is appliedaccording to a different basis.

FIGS. 12A and 12B illustrate exemplary aperiodic SRS subframes of SRSconfigurations.

FIG. 13 illustrates switching of aperiodic SRS configurations accordingto a time point at which a UE receives an aperiodic SRS triggering grantand the aperiodic SRS configurations of FIGS. 12A and 12B.

FIGS. 14A and 14B illustrate fallback aperiodic SRS transmission.

FIGS. 15A to 15C illustrate a method in which cell-specific SRSresources are reused for efficient aperiodic SRS transmission whencell-specific SRS resources (subframes) are allocated at intervals of 2ms.

FIG. 16 illustrates a configuration of a UE-specific periodic SRSsubframe.

FIGS. 17A to 17(c) illustrate an operation for dynamically selectingmultiple SRS configurations using a time relationship between a subframein which an aperiodic SRS triggering grant is received and a subframe inwhich a corresponding aperiodic SRS is transmitted.

FIG. 18 illustrates aperiodic SRS transmission performed whenclassification of the index of a subframe corresponding to the timepoint at which an aperiodic SRS triggering grant is received is appliedaccording to a different basis.

FIGS. 19A and 19B illustrate exemplary aperiodic SRS subframes of SRSconfigurations.

FIG. 20 illustrates switching of aperiodic SRS configuration operationsaccording to a time point at which the UE has received an aperiodic SRStriggering grant and the SRS configurations of FIGS. 19A and 19B.

FIGS. 21A and 21B illustrate aperiodic SRS transmission according to anew scheme in which part of an aperiodic SRS transmission resource isallocated and used as a fallback aperiodic SRS transmission resource.

BEST MODE

Hereinafter, the preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings. It is to beunderstood that the detailed description which will be disclosed withreference to the accompanying drawings is intended to describe theexemplary embodiments of the present invention, and is not intended todescribe a unique embodiment through which the present invention can becarried out. Hereinafter, the detailed description includes detailedmatters to provide full understanding of the present invention. However,it will be apparent to those skilled in the art that the presentinvention can be carried out without the detailed matters. For example,the following description will be made on the assumption that a mobilecommunication system is a 3^(rd) Generation Partnership Project (3GPP)Long Term Evolution (LTE) system, but the present invention isapplicable to other mobile communication systems excluding the uniquematters of the 3GPP LTE system.

In some instances, well-known structures and devices are omitted inorder to avoid obscuring the concepts of the present invention and theimportant functions of the structures and devices are shown in blockdiagram form. The same reference numbers will be used throughout thedrawings to refer to the same or like parts. The exemplary embodiment ofthe specification is not in any way preferable to other embodiments.

In the following description, it is assumed that a terminal includes amobile or fixed user end device such as a user equipment (UE), a mobilestation (MS) and an Advanced Mobile Station (AMS), and a base stationincludes a node of a network end communicating with a terminal, such asa Node-B, an eNode B, a base station, and an Access Point (AP).

In a mobile communication system, a UE or a relay node may receiveinformation from a base station through downlink/backhaul downlink andtransmit information uplink/backhaul uplink. The information transmittedor received by the UE or the relay node includes data and a variety ofcontrol information, and a variety of physical channels is presentaccording to the type and usage of information transmitted or receivedby the UE or the relay node.

Although a wireless communication system including one eNB, one UE, andone relay node is shown for simplicity, the wireless communicationsystem 100 may include one or more eNBs, one or more relay nodes and/orone or more UEs. That is, the base station includes various eNBs such asa macro eNB and a femto eNB and the UE includes various UEs such as amacro UE and a femto UE.

FIG. 1 is a block diagram showing the configuration of a communicationsystem according to the present invention.

The communication system according to the present invention may includean eNB 105, a UE 110 and relay node (not shown). Although thecommunication system 100 including one eNB 105, and one UE 110 is shownfor simplicity, the communication system 100 according to the presentinvention may include a plurality of eNBs and a plurality of UEs.

Referring to FIG. 1, the eNB 105 may include a transmission (Tx) dataprocessor 115, a symbol modulator 120, a transmitter 125, atransmission/reception antenna 130, a processor 180, a memory 185, areceiver 190, a symbol demodulator 195, and a reception (Rx) dataprocessor 197. The UE 110 may include a Tx data processor 165, a symbolmodulator 170, a transmitter 175, a transmission/reception antenna 135,a processor 155, a memory 160, a receiver 140, a symbol demodulator 145and an Rx data processor 165.

Although one antenna 130 or 135 is included in the eNB 105 or the UE110, a plurality of antennas may be included in the eNB 105 or the UE110. Accordingly, the eNB 105 and the UE 110 according to the presentinvention supports Multiple Input Multiple Output (MIMO). The eNB 105and the UE 110 according to the present invention may support bothSingle User (SU)-MIMO and Multi User (MU)-MIMO.

In downlink, the Tx data processor 115 of the eNB 105 receives trafficdata, formats and codes the received traffic data, interleaves andmodulates (or symbol-maps) the coded traffic data, and providesmodulated symbols (data symbols). The symbol modulator 120 receives andprocesses the data symbols and pilot symbols and provides a symbolstream. The symbol modulator 120 of the eNB 105 multiplexes data andpilot symbols and transmits the multiplexed data to the transmitter 125.At this time, each transmitted symbol may be a data symbol, a pilotsymbol or a zero (null) signal value. In each symbol period, pilotsymbols may be consecutively transmitted. The pilot symbols may beFrequency Division Multiplexed (FDM), Orthogonal Frequency DivisionMultiplexed (OFDM), Time Division Multiplexed (TDM) or Code DivisionMultiplexed (CDM) symbols. The transmitter 125 of the eNB 105 receivesthe symbol stream, converts the symbol stream into one or more analogsignals, additionally adjusts (for example, amplifies, filters,frequency up-converts) the analog signals, and generates a downlinksignal suitable for transmission through a radio channel. Subsequently,the downlink signal is transmitted to the the UE 110 through the antenna130.

In the UE 110, the antenna 135 receives the downlink signal from the eNB105 and provides the received signal to the receiver 140. The receiver140 adjusts (for example, filters, amplifies, and frequencydown-converts) the received signal, digitizes the adjusted signal, andacquires samples. The symbol demodulator 145 demodulates the receivedpilot symbols and provides the pilot signals to the processor 155, forchannel estimation.

The symbol demodulator 145 receives a frequency response estimationvalue for downlink from the processor 155, performs data demodulationwith respect to the received data symbols, acquires data symbolestimation values (which are estimation values of the transmitted datasymbols), and provides the data symbol estimation values to the Rx dataprocessor 150. The Rx data processor 150 demodulates (that is,symbol-demaps), deinterleaves and decodes the data symbol estimationvalues and restore the transmitted traffic data.

The processes by the symbol demodulator 145 and the Rx data processor150 are complementary to the processes by the symbol modulator 170 andthe Tx data processor 165 of the eNB 105.

In the UE 110, the Tx data processor 165 processes traffic data andprovides data symbols in uplink. The symbol modulator 170 receives thedata symbols, multiplexes the data symbols with pilot symbols, performsmodulation, and provides a symbol stream to the transmitter 186. Thetransmitter 175 receives and processes the symbol stream, generates anuplink signal, and transmits the uplink signal to the eNB 105 throughthe antenna 135.

In the eNB 105, the uplink signal is received from the UE 110 throughthe antenna 130. The receiver 190 processes the received uplink signaland acquires samples. Subsequently, the symbol demodulator 195 processesthe samples and provides pilot symbols and data symbol estimation valuesreceived in uplink. The Rx data processor 197 processes the data symbolestimation values and restores the traffic data transmitted from the UE110.

The respective processors 180 and 155 of the eNB 105 and the UE 110instruct (for example, control, adjust, or manage) the operations of theeNB 105 and the UE 110, respectively. The processors 180 and 155 may beconnected to the memories 185 and 160 for storing program codes anddata, respectively. The memories 185 and 160 are respectively connectedto the processors 180 and 155 so as to store operating systems,applications and general files.

The processors 180 and 155 may be called controllers, microcontrollers,microprocessors, microcomputers, etc. The processors 180 and 155 may beimplemented by hardware, firmware, software, or a combination thereof.If the embodiments of the present invention are implemented by hardware,Application Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), etc. may be included in the processors 180 and 155.

If the embodiments of the present invention are implemented by firmwareor software, the firmware or software may be configured to includemodules, procedures, functions, etc. for performing the functions oroperations of the present invention. The firmware or software configuredto perform the present invention may be included in the processors 180and 155 or may be stored in the memories 185 and 160 so as to be drivenby the processors 180 and 155.

Layers of the radio interface protocol between the eNB 105 and the UE110 in the wireless communication system (network) may be classifiedinto a first layer (L1), a second layer (L2) and a third layer (L3)based on the three low-level layers of the known Open SystemInterconnection (OSI) model of a communication system. A physical layerbelongs to the first layer and provides an information transport servicethrough a physical channel. A Radio Resource Control (RRC) layer belongsto the third layer and provides control radio resources between the UE110 and the network. The eNB 105 and the UE 110 exchange RRC messageswith each other through a wireless communication network and the RRClayer.

FIG. 2 illustrates the structure of a radio frame in a 3rd GenerationPartnership Project (3GPP) Long Term Evolution (LTE) system as anexample of a mobile communication system.

Referring to FIG. 2, a radio frame includes 10 subframes. A subframeincludes two slots in time domain. A time for transmitting one subframeis defined as a transmission time interval (TTI). For example, onesubframe may have a length of 1 millisecond (ms), and one slot may havea length of 0.5 ms. One slot includes a plurality of orthogonalfrequency division multiplexing (OFDM) symbols in time domain. Since the3GPP LTE uses the OFDMA in the downlink, the OFDM symbol is forrepresenting one symbol period. The OFDM symbol may also be referred toas an SC-FDMA symbol or a symbol period. A resource block (RB) is aresource allocation unit, and includes a plurality of contiguoussubcarriers in one slot. The structure of the radio frame is shown forexemplary purposes only. Thus, the number of subframes included in theradio frame or the number of slots included in the subframe or thenumber of OFDM symbols included in the slot may be modified in variousmanners.

FIG. 3 illustrates the structures of downlink and uplink subframes inthe 3GPP LTE system.

Referring to the FIG. 3(a), a maximum of three OFDM symbols located in afront portion of a 1st slot within a subframe correspond to a controlregion to be assigned with a control channel. The remaining OFDM symbolscorrespond to a data region to be assigned with a physical downlinkshared chancel (PDSCH). Examples of downlink control channels used inthe 3GPP LTE includes a physical control format indicator channel(PCFICH), a physical downlink control channel (PDCCH), a physical hybridARQ indicator channel (PHICH), etc. The PCFICH is transmitted at a firstOFDM symbol of a subframe and carries information regarding the numberof OFDM symbols used for transmission of control channels within thesubframe. The PHICH is a response of uplink transmission and carries anHARQ acknowledgment (ACK)/not-acknowledgment (NACK) signal. Controlinformation transmitted through the PDCCH is referred to as downlinkcontrol information (DCI). The DCI includes uplink or downlinkscheduling information or includes an uplink transmit (Tx) power controlcommand for arbitrary UE groups.

Now, a PDCCH that is a downlink physical channel will be described.

The PDCCH can carry a PDSCH's resource assignment and transport format(referred to as a downlink grant), PUSCH's resource assignmentinformation (referred to as an uplink grant), a transmit power controlcommand for individual UEs within any UE group, activation of a voiceover Internet (VoIP), etc. A plurality of PDCCHs can be transmitted in acontrol region, and the UE can monitor the plurality of PDCCHs. ThePDCCH consists of an aggregation of one or several consecutive controlchannel elements (CCEs). The PDCCH consisting of the aggregation of oneor several consecutive CCEs can be transmitted on a control region afterbeing processed with subblock interleaving. The CCE is a logicalassignment unit used to provide the PDCCH with a coding rate dependingon a wireless channel condition. The CCE corresponds to a plurality ofresource element groups. According to an association relation betweenthe number of CCEs and a coding rate provided by the CCEs, a format ofthe PDCCH and the number of bits of an available PDCCH are determined.

Control information transmitted over the PDCCH is referred to asdownlink control information (DCI). The following table shows the DCIaccording to a DCI format.

TABLE 1 DCI Format Description DCI format 0 used for the scheduling ofPUSCH DCI format 1 used for the scheduling of one PDSCH codeword DCIformat 1A used for the compact scheduling of one PDSCH codeword andrandom access procedure initiated by a PDCCH order DCI format 1B usedfor the compact scheduling of one PDSCH codeword with precodinginformation DCI format 1C used for very compact scheduling of one PDSCHcodeword DCI format 1D used for the compact scheduling of one PDSCHcodeword with precoding and power offset information DCI format 2 usedfor scheduling PDSCH to UEs configured in closed- loop spatialmultiplexing mode DCI format 2A used for scheduling PDSCH to UEsconfigured in open-loop spatial multiplexing mode DCI format 3 used forthe transmission of TPC commands for PUCCH and PUSCH with 2-bit poweradjustments DCI format 3A used for the transmission of TPC commands forPUCCH and PUSCH with single bit power adjustments

A DCI format 0 indicates uplink resource assignment information. DCIformats 1 to 2 indicate downlink resource assignment information. DCIformats 3 and 3A indicate an uplink transmit power control (TPC) commandfor any UE groups.

A method for allowing a BS to perform resource mapping for PDCCHtransmission in the 3GPP LTE system will hereinafter be described indetail.

Generally, the BS may transmit scheduling allocation information andother control information over the PDCCH. Information about a physicalcontrol channel (PCCH) is configured in the form of one aggregate (oneaggregation) or several CCEs, such that the resultant information istransmitted as one aggregate or several CCEs. Namely, a PDCCHtransmission unit of the BS is a CCE. One CCE includes 9 resourceelement groups (REGs). The number of RBGs unallocated to either PhysicalControl Format Indicator Channel (PCFICH) or Physical Hybrid AutomaticRepeat Request Indicator Channel (PHICH) is N_(REG). CCEs from 0 toN_(CCE)−1 may be available to a system (where, N_(CCE)=└N_(REG)/9┘).PDCCH supports multiple formats as shown in the following Table 3. OnePDCCH composed of n contiguous CCEs begins with a CCE having ‘i mod n=0’(where ‘i’ is a CCE number). Multiple PDCCHs may be transmitted throughone subframe.

TABLE 2 PDCCH Number of Number of resource- Number of format CCEselement groups PDCCH bits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

Referring to Table 2, a base station (BS) may decide a PDCCH formataccording to how many regions are required for the BS to transmitcontrol information. The UE reads control information and the like inunits of a CCE, resulting in reduction of overhead. Likewise, the relaynode (RN) may also read control information and the like in units of aRelay-CCE (R-CCE). In the LTE-A system, in order to allow the BS totransmit R-PDCCH information for an arbitrary RN, a resource element(RE) may be mapped in units of a Relay-Control Channel Element (R-CCE).

Referring to the FIG. 3(b), an uplink subframe can be divided in afrequency domain into a control region and a data region. The controlregion is allocated with a physical uplink control channel (PUCCH) forcarrying uplink control information. The data region is allocated with aphysical uplink shared channel (PUSCH) for carrying user data. Tomaintain a single carrier property, one UE does not simultaneouslytransmit the PUCCH and the PUSCH. The PUCCH for one UE is allocated toan RB pair in a subframe. RBs belonging to the RB pair occupy differentsubcarriers in respective two slots. This is called that the RB pairallocated to the PUCCH is frequency-hopped in a slot boundary.

FIG. 4 illustrates a downlink time-frequency resource grid structureaccording to the present invention.

Referring to the FIG. 4, the transmitted signal in each slot isdescribed by a resource grid of N_(RB) ^(DL)×N_(SC) ^(RB) subcarriersand N_(symb) ^(DL) OFDM symbols. Here, N_(RB) ^(DL) represents for thenumber of resource blocks (RBs) for downlink, N_(SC) ^(RB) representsfor the number of subcarriers constituting a RB, and N_(symb) ^(DL)represents for the number of OFDM symbols in a downlink slot. Thequantity N_(RB) ^(DL) depends on the downlink transmission bandwidthconfigured in the cell and shall fulfill N_(RB) ^(min,DL)≦N_(RB)^(DL)≦N_(RB) ^(max,DL) where N_(RB) ^(min,DL) and N_(RB) ^(max,RB),though not limited to these values, are the smallest and largestdownlink bandwidth, respectively. Here, N_(RB) ^(min,DL) is the minimumdownlink bandwidth and N_(RB) ^(max,RB) the maximum downlink bandwidthsupported by the wireless communication system. The number of OFDMsymbols in a slot depends on the cyclic prefix (CP) length andsubcarrier spacing. In case of multi-antenna transmission, there may beone resource grid defined per antenna port.

Each element in the resource grid for antenna port p is called aresource element and is uniquely identified by the index pair (k,l) in aslot where k=0, . . . , N_(RB) ^(DL)N_(SC) ^(RB)−1 and l=0, . . . ,N_(symb) ^(DL)−1 are the indices in the frequency and time domains,respectively.

Resource blocks shown in FIG. 4 are used to describe the mapping ofcertain physical channels to resource elements. RB is classified intophysical resource block (PRB) and virtual resource block (VRB).

A physical resource block is defined as N_(symb) ^(DL) consecutive OFDMsymbols in the time domain and N_(SC) ^(RB) consecutive subcarriers inthe frequency domain, where N_(symb) ^(DL) and N_(SC) ^(RB) may be givenby Table 3. A physical resource block thus consists of N_(symb)^(DL)×N_(sc) ^(RB) resource elements, corresponding to one slot in thetime domain and 180 kHz in the frequency domain, though not limited tothese values.

TABLE 3 Configuration N_(sc) ^(RB) N_(symb) ^(DL) Normal Δf = 15 kHz 127 cyclic prefix Extended Δf = 15 kHz 6 cyclic Δf = 7.5 kHz 24 3 prefix

Physical resource blocks are numbered from 0 to N_(RB) ^(DL)−1 in thefrequency domain. The relation between the physical resource blocknumber in the frequency domain and resource elements (k,l) in a slot isgiven by

$n_{PRB} = {\left\lfloor \frac{k}{N_{sc}^{RB}} \right\rfloor.}$

A VRB can have the same size as that of the PRB. There are two types ofVRBs defined, the first one being a localized type and the second onebeing a distributed type. For each VRB type, a pair of VRBs have asingle VRB index in common (may hereinafter be referred to as a ‘VRBnumber’) and are allocated over two slots of one subframe. In otherwords, N_(RB) ^(DL) VRBs belonging to a first one of two slotsconstituting one subframe are each assigned any one index of 0 to N_(RB)^(DL)−1, and N_(RB) ^(DL) VRBs belonging to a second one of the twoslots are likewise each assigned any one index of 0 to N_(RB) ^(DL)−1.

Hereinafter, the general MIMO technology will be described. The MIMOtechnology is an abbreviation of the Multi-Input Multi-Outputtechnology. The MIMO technology uses multiple transmission (Tx) antennasand multiple reception (Rx) antennas to improve the efficiency of Tx/Rxdata, whereas a previously conventional technique has generally used asingle transmission (Tx) antenna and a single reception (Rx) antenna. Inother words, the MIMO technology allows a transmission end or receptionend of a wireless communication system to use multiple antennas(hereinafter referred to as a multi-antenna), so that the capacity orperformance can be improved. For the convenience of description, theterm “MIMO” can also be considered to be a multi-antenna technology.

In more detail, the MIMO technology is not dependent on a single antennapath to receive a single total message, collects a plurality of datapieces received via several antennas, and completes total data. As aresult, the MIMO technology can increase a data transfer rate within aspecific range, or can increase a system range at a specific datatransfer rate.

The next-generation mobile communication technology requires a higherdata transfer rate than that of a conventional mobile communicationtechnology, so that it is expected that the effective MIMO technology isrequisite for the next-generation mobile communication technology. Underthis assumption, the MIMO communication technology is thenext-generation mobile communication technology to be applied to mobilecommunication terminals or repeaters, and can extend the range of a datacommunication range, so that it can overcome the limited amount oftransfer data of other mobile communication systems due to a variety oflimited situations.

In the meantime, the MIMO technology from among a variety oftechnologies capable of improving the transfer efficiency of data cangreatly increase an amount of communication capacity and Tx/Rxperformances without allocating additional frequencies or increasing anadditional power. Due to these technical advantages, most companies ordevelopers are intensively paying attention to this MIMO technology.

FIG. 5 illustrates an exemplary of general multiple antennascommunication.

Referring to FIG. 5, if the number of transmission (Tx) antennasincreases to N_(T), and at the same time the number of reception (Rx)antennas increases to N_(R), a theoretical channel transmission capacityof the MIMO communication system increases in proportion to the numberof antennas, differently from the above-mentioned case in which only atransmitter or receiver uses several antennas, so that a transfer rateand a frequency efficiency can greatly increase.

In this case, the transfer rate acquired by the increasing channeltransmission capacity is equal to the multiplication of a maximumtransfer rate (R_(o)) acquired when a single antenna is used and a rateincrement (R_(i)), and can theoretically increase. The rate increment(R_(i)) can be represented by the following equation 1:R _(i)=min(N _(T) ,N _(R))   [Equation 1]

A mathematical modeling of a communication method for use in theabove-mentioned MIMO system will hereinafter be described in detail.Firstly, as can be seen from FIG. 2-6, it is assumed that N_(T) Txantennas and N_(R) Rx antennas exist. In the case of a transmission (Tx)signal, a maximum number of transmission information pieces is N_(T)under the condition that N_(T) Tx antennas are used, so that the Txsignal can be represented by a specific vector shown in the followingequation 2:s=[s₁, s₂, . . . , s_(N) _(T) ]^(T)   [Equation 2]

In the meantime, individual transmission information pieces (s₁, s₂, . .. , s_(NT)) may have different transmission powers. In this case, if theindividual transmission powers are denoted by (P₁, P₂, . . . , P_(NT)),transmission information having an adjusted transmission power can berepresented by a specific vector shown in the following equation 3:ŝ=[ŝ₁, ŝ₂, . . . , ŝ_(N) _(T) ]^(T)=[P₁s₁, P₂s₂, . . . , P_(N) _(T)s_(N) _(T) ]^(T)   [Equation 3]

In Equation 3, ŝ is a diagonal matrix of a transmission power, and canbe represented by the following equation 4:

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In the meantime, the information vector ŝ having an adjustedtransmission power is multiplied by a weight matrix (W), so that N_(T)transmission (Tx) signals (x₁, x₂, . . . , x_(NT)) to be actuallytransmitted are configured. In this case, the weight matrix is adaptedto properly distribute Tx information to individual antennas accordingto Tx-channel situations. The above-mentioned Tx signals (x₁, x₂, . . ., x_(NT)) can be represented by the following equation 5 using thevector (x):

$\begin{matrix}{x = {\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {\quad{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{12} & w_{22} & \ldots & w_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix} = {\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix} = {{W\hat{s}} = {WPs}}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In Equation 5, w_(ij) is a weight between the i-th Tx antenna and thej-th Tx information, and W is a matrix indicating the weight w_(ij). Thematrix W is called a weight matrix or a precoding matrix. In themeantime, the above-mentioned Tx signal (x) can be considered indifferent ways according to two cases, i.e., a first case in which thespatial diversity is used and a second case in which the spatialmultiplexing is used. In the case of using the spatial multiplexing,different signals are multiplexed and the multiplexed signals aretransmitted to a destination, so that elements of the information vector(s) have different values.

Otherwise, in the case of using the spatial diversity, the same signalis repeatedly transmitted via several channel paths, so that elements ofthe information vector (s) have the same value. Needless to say, thecombination of the spatial multiplexing scheme and the spatial diversityscheme may also be considered. In other words, the same signal istransmitted via three Tx antennas according to the spatial diversityscheme, and the remaining signals are spatially multiplexed and thentransmitted to a destination. Next, if N_(R) Rx antennas are used, Rxsignals (y₁, y₂, . . . , y_(NR)) of individual antennas can berepresented by a specific vector (y) shown in the following equation 6:y=[y₁, y₂, . . . , y_(N) _(R) ]^(T)   [Equation 6]

In the meantime, if a channel modeling is executed in the MIMOcommunication system, individual channels can be distinguished from eachother according to Tx/Rx antenna indexes. A specific channel passing therange from a Tx antenna (j) to an Rx antenna (i) is denoted by h_(ij).In this case, it should be noted that the index order of the channelh_(ij) is located before an Rx-antenna index and is located after aTx-antenna index. Several channels are tied up, so that they aredisplayed in the form of a vector or matrix. An exemplary vector is asfollows.

FIG. 6 shows channels from N_(T) Tx antennas to an Rx antenna (i).Referring to FIG. 6, the channels passing in the range from the N_(T) Txantennas to the Rx antenna (i) can be represented by the followingequation 7:h_(i) ^(T)=[h_(i1), h_(i2), . . . , h_(iN) _(T) ]   [Equation 7]

If all channels passing in the range from the N_(T) Tx antennas to N_(R)Rx antennas are denoted by the matrix shown in Equation 7, the followingequation 8 is acquired:

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1\; N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1}^{T} & h_{N_{R}2}^{T} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

In the meantime, an Additive White Gaussian Noise (AWGN) is added to anactual channel which has passed the channel matrix H shown in Equation8. The AWGN (n₁, n₂, . . . , n_(NR)) added to each of N_(R) Rx antennascan be represented by a specific vector shown in the following equation9:n=[n₁, n₂, . . . , n_(N) _(R) ]^(T)   [Equation 9]

By the above-mentioned modeling method of the Tx signal, Rx signal, andAWGN, each MIMO communication system can be represented by the followingequation 10:

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1\; N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{T}}\end{bmatrix}} = {{Hx} + n}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

In the meantime, the number of rows and the number of columns of achannel matrix H indicating a channel condition is determined by thenumber of Tx/Rx antennas. In the channel matrix H, the number of rows isequal to the number (N_(R)) of Rx antennas, and the number of columns isequal to the number (N_(T)) of Tx antennas. Namely, the channel matrix His denoted by N_(R)×N_(T) matrix.

Generally, a matrix rank is defined by a smaller number between thenumber of rows and the number of columns, in which the rows and thecolumns are independent of each other. Therefore, the matrix rank cannotbe higher than the number of rows or columns. The rank of the channelmatrix H can be represented by the following equation 11:rank(H)≦min(N _(T) ,N _(R))   [Equation 11]

A downlink reference signal will hereinafter be described in detail.

The downlink reference signal includes a common reference signal (CRS)shared among all UEs contained in a cell and a dedicated referencesignal (DRS) assigned to a specific UE. In the 3GPP LTE-A system or thelike, the DRS may also be referred to as a demodulation RS (DM RS).

The common reference signal (CRS) may be used to acquire channel statusinformation and perform handover measurement. The dedicated referencesignal (DRS) may be used to demodulate data. The CRS may be acell-specific reference signal, and the DRS may be a UE-specificreference signal.

The UE measures the CRS and informs the BS of channel feedbackinformation (e.g., Channel Quality Information (CQI), Precoding MatrixIndicator (PMI), and Rank Indicator (RI)). The BS performs downlinkfrequency scheduling using feedback information received from the UE.

In order to transmit the aforementioned reference signals to the UE, theBS performs resource allocation in consideration of the amount of radioresources to be allocated to each reference signal, exclusive positionof the CRS and the DRS, position of a synchronous channel (SCH) and abroadcast channel (BCH), the DRS density, and the like.

In this case, provided that a relatively large amount of resources isassigned to each reference signal, a data transmission rate isrelatively deteriorated whereas channel estimation performance isincreased. Provided that a relatively small amount of resources isassigned to each reference signal, a reference signal density is loweredwhereas a data transmission rate is increased, resulting indeterioration of channel estimation performance. Effective resourceallocation of each reference signal in consideration of channelestimation, data transmission rate, etc. is of importance to systemperformance.

FIG. 7 is a conceptual diagram illustrating a reference signal (RS)structure for use in a downlink (DL) subframe according to oneembodiment of the present invention, and shows a subframe structuremapped to a reference signal in a system capable of supporting a maximumof 4 antennas.

Referring to FIG. 7, one downlink subframe is composed of two time slotsin a time domain, reference number ‘1’ represents a symbol index of eachslot, and the initial three symbols are assigned to a controlinformation region. In addition, a reference signal (RS) is mapped inunits of one resource block in a frequency domain, and the mappedresultant RS is repeatedly transmitted.

In FIG. 7, the number of OFDM symbols contained in one slot may bechanged according to a cyclic prefix (CP) construction. FIG. 7(a) showsOFDM symbols for use with a normal CP. In FIG. 7(a), the number of OFDMsymbols contained in one slot is 7. FIG. 7(b) shows OFDM symbols for usein the extended CP. In FIG. 7(b), the length of one OFDM symbol isincreased, such that the number of OFDM symbols contained in one slot isless than that of a normal CP, for example, the number of OFDM symbolsmay be set to 6.

Reference elements (REs) 0, 1, 2 and 3 (where, 0, 1, 2, 3 and 4represent R0, R1, R2 and R3 corresponding to RS per antenna portrespectively) from among resource elements (REs) contained in theresource block (RB) shown in FIG. 7(a) or 7(b) represent cell-specificcommon reference signal (CRS) for four antenna ports. The REs 0, 1, 2and 3 are adapted to measure a status of a channel transmitted througheach antenna port 0, 1, 2 or 3 as well as to demodulate data transmittedto each port 0, 1, 2 or 3. Reference symbol ‘D’ represents a UE-specificdedicated reference signal (DRS), and is adapted to demodulate datatransmitted over PDSCH. Information about the presence or absence of theDRS is transmitted to the UE via higher-layer signaling. Thisinformation corresponds to an effective resource element (RE) only inthe case of a UE to which the corresponding PDSCH is allocated.

If the common reference signal (CRS) is mapped to time-frequency regionresources, mapping of the CRS for one antenna port is performed atintervals of 6 REs in a frequency domain, and the CRS mapping result istransmitted at intervals of 6 REs. Therefore, one RB is composed of atotal of 12 REs in a frequency domain, and two REs are used per antennaport.

On the other hand, RS mapping rules into resource block are following asEquation 12

$\begin{matrix}{{k = {{6m} + {\left( {v + v_{shift}} \right){mod}\mspace{14mu} 6}}}{l = \left\{ {{{\begin{matrix}{0,{N_{symb}^{DL} - 3}} & {{{if}\mspace{14mu} p} \in \left\{ {0,1} \right\}} \\1 & {{{if}\mspace{14mu} p} \in \left\{ {2,3} \right\}}\end{matrix}m} = 0},1,\ldots\;,{{{2 \cdot N_{RB}^{DL}} - {1m^{\prime}}} = {{m + N_{RB}^{\max,{DL}} - {N_{RB}^{DL}v}} = \left\{ {{\begin{matrix}0 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\3 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\3 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\0 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\{3\left( {n_{s}{mod}\mspace{14mu} 2} \right)} & {{{if}\mspace{14mu} p} = 2} \\{3 + {3\left( {n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} \right)}} & {{{if}\mspace{14mu} p} = 3}\end{matrix}v_{shift}} = {N_{ID}^{cell}{mod}\mspace{14mu} 6}} \right.}}} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack \\{{k = {{\left( k^{\prime} \right){mod}\mspace{14mu} N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \left\{ {{\begin{matrix}{{4m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} \in \left\{ {2,3} \right\}} \\{{4m^{\prime}} + {\left( {2 + v_{shift}} \right){mod}\mspace{14mu} 4}} & {{{if}\mspace{14mu} l} \in \left\{ {5,6} \right\}}\end{matrix}l} = \left\{ {{\begin{matrix}3 & {l^{\prime} = 0} \\6 & {l^{\prime} = 1} \\2 & {l^{\prime} = 2} \\5 & {l^{\prime} = 3}\end{matrix}l^{\prime}} = \left\{ {{{\begin{matrix}{0,1} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} = 0} \\{2,3} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\;,{{3N_{RB}^{PDSCH}} - 1}} \right.} \right.} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack \\{{k = {{\left( k^{\prime} \right){mod}\mspace{11mu} N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \left\{ {{\begin{matrix}{{3m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} = 4} \\{{3m^{\prime}} + {\left( {2 + v_{shift}} \right)\mspace{11mu}{mod}\mspace{14mu} 3}} & {{{if}\mspace{14mu} l} = 1}\end{matrix}l} = \left\{ {{\begin{matrix}4 & {l^{\prime} \in \left\{ {0,2} \right\}} \\1 & {l^{\prime} = 1}\end{matrix}l^{\prime}} = \left\{ {{{\begin{matrix}0 & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} = 0} \\{1,2} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\mspace{14mu} 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\;,{{{4N_{RB}^{PDSCH}} - {1v_{shift}}} = {N_{ID}^{cell}\mspace{11mu}{mod}\mspace{14mu} 3}}} \right.} \right.} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

In equations 12 to 14, k and p mean subcarrier index and antenna port.And N_(RB) ^(DL), n_(s), N_(ID) ^(cell) mean number of RB allocated forDL, slot index, cell ID. Note that given RS positioning depends onV-shift values in terms of frequency domain.

It is expected that the LTE-A system which is the standard of the nextgeneration mobile communication system will support a coordinated multipoint (CoMP) system, which is not supported in the existing standard, toimprove a data transmission rate. In this case, the CoMP system meansthat a system in which two or more base stations or cells performcommunication with a user equipment in cooperation with each other toimprove communication throughput between a user equipment located in ashade zone and a base station (cell or sector).

The CoMP system can be classified into a CoMP-joint processing (CoMP-JP)system of cooperative MIMO type through data sharing and aCoMP-coordinated scheduling/beamforming (CoMP-CS/CB) system.

In case of the downlink, according to the CoMP-JP system, the userequipment can simultaneously receive data from each base station thatperforms CoMP, and can improve receiving throughput by combining signalsreceived from each base station with one another. Unlike the CoMP-JPsystem, according to the CoMP-CS/CB system, the user equipment canreceive data from one base station through beamforming.

In case of the uplink, according to the CoMP-JP system, each basestation can simultaneously receive a PUSCH signal from the userequipment. Unlike the CoMP-JP system, according to the CoMP-CS/CBsystem, only one base station can receive a PUSCH. In this case, theCoMP-CS/CB system is determined by cooperative cells (or base stations).

MU-MIMO technology is that eNode B allocates each antenna resource touser equipments and schedule by selecting user equipment which cantransmit at higher data rate per antenna. MU-MIMO technology improvessystem throughput.

FIG. 8 illustrates an exemplary uplink subframe configuration includingan SRS symbol.

Referring to FIG. 8, the SRS, which are not associated with uplink dataand/or control transmission, are primarily used for channel qualityestimation to enable frequency-selective scheduling on the uplink.However, they can be used for other purposes such as to enhance powercontrol or to support various start-up functions for UEs not recentlyscheduled. SRS is reference signal used for uplink channel, is pilotsignal transmitted by eNode B to user equipment, and is used formeasuring channel state between user equipment and eNode B. Channel fortransmitting SRS may have different transmission bandwidth andtransmission period per user equipment according to state of userequipment. The eNode B may determine that scheduling data channel ofwhich user equipment in every subframe.

Some examples include initial Modulation and Coding Scheme (MCS)selection, initial power control for data transmissions, timing advance,and so-called frequency semi-selective scheduling in which the frequencyresource is assigned selectively for the first slot of a subframe andhops pseudorandomly to a different frequency in the second slot.

An SRS can be used for downlink channel quality estimation under anassumption that a wireless channel is reciprocal between the uplink anddownlink. This assumption is valid in a time division duplex (TDD)system where the uplink and downlink share the same frequency spectrumand are separated in time domain. Subframes in which SRSs aretransmitted by a UE within a cell may be indicated by cell-specificbroadcast signaling. A 4-bit cell-specific parameter‘srssubframeConfiguration’ indicates 15 possible sets of subframes inwhich an SRS may be transmitted within each radio frame. Thisconfiguration provides flexibility in adjusting SRS overhead. As shownin FIG. 9, an SRS may be transmitted in the last SC-FDMA symbol in suchconfigured subframes.

Thus, the SRS and DeModulation Reference Signal (DM RS) are located indifferent SC-FDMA symbols in a subframe. SRSs of a number of UEs thatare transmitted in last SC-FDMA symbols of the same subframes can bediscriminated according to the frequency locations. Since PUSCH data isnot transmitted through an SC-FDMA symbol designated for SRS, everysubframe has an SRS symbol in the worst case, causing a soundingoverhead of 7%.

An SRS is generated using a Constant Amplitude Zero Auto Correlation(CAZAC) sequence or the like. SRSs transmitted from a number of UEs areCAZAC sequences r^(SRS)(n)=r_(u,v) ^((α))(n) having different cyclicshift values α according to the following Equation 15. Here, r^(SRS)(n)is an SRS sequence.

$\begin{matrix}{\alpha = {2\pi\frac{n_{SRS}^{cs}}{8}}} & \left\lbrack {{Equation}\mspace{14mu} 15} \right\rbrack\end{matrix}$

Here, n_(SRS) ^(cs) is a value set for each UE by the higher layer andhas an integer value between 0 and 7. Each CAZAC sequence generated fromone CAZAC sequence through cyclic shifting has zero correlation withother CAZAC sequences having cyclic shift values different from itscyclic shift value. Using these characteristics, SRSs of the samefrequency region can be discriminated according to the sequence CAZACsequence cyclic shift values. An SRS of each UE is allocated to afrequency according to a parameter set by the eNodeB. The UE performsfrequency hopping of the SRS to allow the SRS to be transmitted over theoverall uplink data transfer bandwidth.

As described above, a 3GPP LTE Release 8/9 system supports only periodicSRS transmission of UEs. This allows the eNodeB to estimate uplinkchannel quality of each UE. Here, the channel estimated by the eNodeB isused for functions such as frequency dependent scheduling, link leveladaptation, timing estimation, and UL power control. The eNodeB maytransmit an SRS uplink configuration to each UE through higher layersignaling (for example, RRC signaling) or the like in a UE-specific orcell-specific manner using an SRS parameter. The eNodeB may notify theUE of SRS uplink configuration information through an SRS uplinkconfiguration information element message type as shown in the followingTable 4.

TABLE 4 SoundingRS-UL-Config information element -- ASN1STARTSoundingRS-UL-ConfigCommon ::= CHOICE { release NULL, setup SEQUENCE {srs-BandwidthConfig ENUMERATED {bw0, bw1, bw2, bw3, bw4, bw5, bw6, bw7},srs-SubframeConfig ENUMERATED { sc0, sc1, sc2, sc3, sc4, sc5, sc6, sc7,sc8, sc9, sc10, sc11, sc12, sc13, sc14, sc15},ackNackSRS-SimultaneousTransmission BOOLEAN, srs-MaxUpPts ENUMERATED{true} OPTIONAL -- Cond TDD } } SoundingRS-UL-ConfigDedicated ::=CHOICE{ release NULL, setup SEQUENCE { srs-Bandwidth ENUMERATED {bw0,bw1, bw2, bw3}, srs-HoppingBandwidth ENUMERATED (hbw0, hbw1, hbw2,hbw3), freqDomainPosition INTEGER (0..23), duration BOOLEAN,srs-ConfigIndex INTEGER (0..1023), transmissionComb INTEGER (0..1),cyclicShift ENUMERATED {cs0, cs1, cs2, cs3, cs4, cs5, cs6, cs7} } } --ASN1STOP

The following Table 5 shows SRS configuration parameters included in aSoundingRS-UL-Config information element message type in the above Table4.

TABLE 5 Sounding RS parameter Signalling name Significance typesrsBandwidthConfiguration Maximum SRS bandwidth Cell specific in thecell srsSubframeConfiguration Sets of subframes in which Cell-specificSRS may be transmitted in the cell srsBandwidth SRS transmissionbandwidth UE-specific for a UE frequencyDomainPosition Frequency-domainposition UE-specific srsHoppingBandwidih Frequency hop size UE-specificDuration Single SRS or periodic UE-specific srsConfigurationIndexPeriodicity and subframe UE-specific offset transmissionCombTransmission comb offset UE-specific if^(CS) _(SRS) Cyclic shiftUE-specific

As shown in Tables 4 and 5, the SRS configuration information that theeNodeB provides to the UE may include, as SRS configuration parameters,an srsBandwidthConfiguration parameter, srsSubframeConfigurationparameter, an srsBandwidth parameter, a frequencyDomainPositionparameter, an SrsHoppingBandwidth parameter, a duration parameter, ansrsConfigurationIndex parameter, and a transmissionComb parameter. ThesrsBandwidthConfiguration parameter represents maximum SRS bandwidthinformation in the cell and srsSubframeConfiguration parameterrepresents information of sets of subframes in which the UE may transmitan SRS in the cell. The eNodeB may notify the UE of thesrsSubframeConfiguration parameter through cell-specific signaling. Asshown in Table 4, the eNodeB may signal the srsSubframeConfigurationparameter in a 4-bit size (indicating sc0, sc1, sc2, sc3, sc4, sc5, sc6,sc7 sc8 sc9 sc10, sc11, sc12, sc13, sc14, and sc15) to the UE. ThesrsBandwidth parameter represents an SRS transmission bandwidth for theUE, the frequencyDomainPosition parameter represents a position in thefrequency domain, the SrsHoppingBandwidth parameter represents an SRSfrequency hop size, the duration parameter represents whether SRStransmission is single or periodic SRS transmission. ThesrsConfigurationIndex parameter represents periodicity and a subframeoffset (for example, a time unit corresponding to an interval betweenthe first subframe and a subframe in which the first SRS is transmittedin a frame), and the transmissionComb parameter represents atransmission comb offset.

The eNodeB may notify the UE of the srsBandwidthConfiguration parameterand the srsSubframeConfiguration parameter through cell-specificsignaling. On the contrary, the eNodeB may individually notify each UEof the srsBandwidth parameter, the frequencyDomainPosition parameter,the SrsHoppingBandwidth parameter, the duration parameter, thesrsConfigurationIndex parameter, and the transmissionComb parameterthrough UE-specific signaling.

The 3GPP LTE Release 10 system supports aperiodic SRS transmission formore adaptive uplink channel quality estimation and more efficient useof SRS resources than the conventional system. A method for triggeringaperiodic SRS transmission is currently under discussion. For example,the eNodeB may perform triggering using a DL/UL grant in a PDCCH. Thatis, the eNodeB may transmit an aperiodic SRS transmission triggeringindicator for triggering aperiodic SRS transmission of the UE through aDL grant or a UL grant including the indicator or may transmit theindicator in a newly defined message format. The present invention willnow be described with reference to an aperiodic SRS triggering grant (oraperiodic SRS triggering indicator) as an example of a message fortriggering aperiodic SRS transmission of the UE.

In the present invention, the eNodeB may provide information regardingmultiple aperiodic SRS configurations to the UE through higher layersignaling. The multiple aperiodic SRS configuration informationtransmitted by the eNodeB may include index information of a subframe inwhich an aperiodic SRS triggering grant is received or information suchas information regarding a time relationship between a subframe in whichan aperiodic SRS triggering grant is received and a subframe in which acorresponding aperiodic SRS is transmitted and information regardingresources for aperiodic SRS transmission. The present invention suggeststhat the UE selectively apply multiple aperiodic SRS configurations.Especially, the UE may adaptively switch aperiodic SRS configurationsusing the index information of a subframe in which an aperiodic SRStriggering grant is received or the time relationship between a subframein which an aperiodic SRS triggering grant is received and a subframe inwhich a corresponding aperiodic SRS is transmitted.

Here, the number of aperiodic SRS configurations may vary depending onthe basis of classification of the index of a subframe corresponding tothe time point at which an aperiodic SRS triggering grant arrives or thedefinition of the time relationship between a subframe in which theaperiodic SRS triggering grant has been received and a subframe in whichthe corresponding aperiodic SRS has been transmitted. This methodsuggested in the present invention has an advantage in that the methoddoes not require additional signaling for aperiodic SRS configurationswitching and can also efficiently solve both the SRS coverage problemand the co-channel Heterogeneous Network (HetNet) uplink signalinterference problem through adaptive aperiodic SRS configurationswitching.

First, it is possible to consider that cell-specific periodic SRSresources, UE-specific aperiodic SRS resources, and UE-specific periodicSRS resources, which are defined in the 3GPP LTE Release 8/9 system, arereused as resources for aperiodic SRS transmission in the suggestedmethod. Accordingly, this method decreases overhead required forsignaling SRS resource position information and enables efficient use ofSRS resources, compared to methods in which additional new aperiodic SRSresources are defined.

Aperiodic SRS configurations that the eNodeB transmits through higherlayer signaling may be variously defined as parameters such as SRSbandwidth, comb, hopping bandwidth, and start Physical Resource Block(PRB) allocation have various values.

The suggested method has an advantage in that it is possible to moreefficiently cope with changes in the state of an uplink channel betweenthe eNodeB and the UE since whether or not aperiodic SRS transmission isperformed is not only merely determined through the aperiodic SRStriggering grant but the UE also adaptively switches multiple aperiodicSRS configurations. Specifically, in a situation such as an HetNetsituation, an appropriate aperiodic SRS configuration may vary accordingto the position of the UE. In order to cover this, the eNodeB needs toprovide information regarding multiple aperiodic SRS configurations andinformation regarding resources of the multiple aperiodic SRSconfigurations and the processor 255 of the UE needs to appropriatelyselect one of the multiple aperiodic SRS configurations and to operateaccordingly. For example, the UE may use an aperiodic SRS configurationtied with a subframe in which a PDCCH including a UL grant (for example,a UL grant for triggering aperiodic SRS transmission or a UL grant fortriggering PUSCH transmission) is received according to the receivedtiming of the PDCCH.

The following is a description of the time point at which the UEtransmits an aperiodic SRS. Assuming that the UE has received anaperiodic SRS triggering grant in subframe n (i.e., a subframe whoseindex is “n”) of a specific frame, the time point at which the UEtransmits an aperiodic SRS corresponds to, for example, a cell-specificperiodic SRS subframe closest to the subframe n or a closestcell-specific periodic SRS subframe after subframe n+3. The UE mayperform aperiodic SRS transmission not only through such cell-specificaperiodic SRS resources but also through UE-specific aperiodic SRSresources and UE-specific periodic SRS resources. The time point ofaperiodic SRS transmission of the UE is not limited to these subframes.

In the case where aperiodic SRS transmission time points of differentUEs overlap and available aperiodic SRS resources are insufficient,higher priority may be given to aperiodic SRS transmission taking intoconsideration aperiodic SRS bandwidths, aperiodic SRS transmissionperiods, and the like of the UEs.

FIGS. 9A and 9B illustrate an exemplary subframe for cell-specificperiodic SRS transmission and an exemplary subframe for UE-specificperiodic SRS transmission.

As shown in FIG. 9A, the eNodeB may configure periodic SRS subframes(subframes 1, 3, 5, 7, and 9), which are slash-hatched in FIG. 9A, inthe specific frame, at intervals of 2 ms according to a cell-specificperiodic SRS configuration.

FIG. 9B shows a UE-specific periodic SRS configuration. The eNodeB mayallocate a part of a subframe set including cell-specific periodic SRSsubframes as a UE-specific periodic SRS subframe to a specific UE. Asshown in FIG. 9B, for example, the eNodeB allocates periodic SRSsubframes (subframes 1, 5, and 9) to a specific UE at intervals of 4 msaccording to a UE-specific periodic SRS configuration. In this case, thespecific UE to which the eNodeB has allocated the UE-specific periodicSRS subframe, may transmit periodic UE-specific SRSs in subframes ofsubframe indices 1, 5, and 9, which are dot-hatched in FIG. 9B, in thespecific frame.

FIGS. 10A, 10B, and 10C illustrate exemplary operations for adaptivelyselecting multiple SRS configurations using a time relationship betweena subframe in which an aperiodic SRS triggering grant is received and asubframe in which a corresponding aperiodic SRS is transmitted.

In FIGS. 10A, 10B, and 10C, it is assumed that the eNodeB has configuredsubframes 1, 3, 5, 7, and 9 as cell-specific periodic SRS subframes andhas configured subframes 1, 5, and 9 as UE-specific periodic SRSsubframes.

The eNodeB may set multiple aperiodic SRS configurations and notify a UEof the aperiodic SRS configurations. Here, these aperiodic SRSconfigurations are referred to as a first aperiodic SRS configurationand a second aperiodic SRS configuration. The eNodeB notifies the UE ofinformation regarding such multiple aperiodic SRS configurations throughhigher layer signaling. The aperiodic SRS configuration information mayinclude information regarding the time point at which the UE transmitsan aperiodic SRS and information regarding resources for aperiodic SRStransmission. For example, the time point at which the UE transmits anaperiodic SRS may be a cell-specific periodic SRS subframe which isclosest to (or earliest from) subframe n in which an aperiodic SRStriggering grant is received or a cell-specific periodic SRS subframewhich first comes after subframe n+3. In addition, a periodic SRS may betransmitted not only through a cell-specific SRS resource but alsothrough a UE-specific aperiodic SRS resource and a UE-specific SRSperiodic resource. The present invention is described as follows, forexample, assuming that the aperiodic SRS configuration has been set suchthat the time point at which the UE transmits an aperiodic SRS is acell-specific periodic SRS subframe which is closest to a subframe(subframe n) in which an aperiodic SRS triggering grant is received. Inthe following description, it is also assumed that a cell-specificperiodic SRS transmission subframe is set at intervals of, for example,2 ms as illustrated in FIG. 9A.

The second SRS configuration is set such that the UE transmits anaperiodic SRS in subframe n+2 in response to an aperiodic SRS triggeringgrant received in subframe n (n=1, 2, . . . ). The first SRSconfiguration is set such that the UE transmits an aperiodic SRS insubframe n+2 in response to an aperiodic SRS triggering grant receivedin subframe n+1. In this manner, the processor 255 of the UE may selecta specific SRS configuration from multiple SRS configurations based on atime relation between a subframe in which an aperiodic SRS triggeringgrant is received and a corresponding aperiodic SRS transmissionsubframe and may perform an operation corresponding to the selected SRSconfiguration. Here, for example, let us assume that one frame includes10 subframes and subframe indices 1 to 10 are assigned respectively tothe 10 subframes included in one frame.

Referring to FIG. 10A, according to the second aperiodic SRSconfiguration, the UE may be configured such that, when the timerelation between a subframe in which an aperiodic SRS triggering grantis received and a corresponding aperiodic SRS transmission subframe(i.e., the index difference between the subframe in which the aperiodicSRS triggering grant is received and the corresponding aperiodic SRStransmission subframe) is 2, the UE transmits an aperiodic SRS for anaperiodic SRS triggering grant received in subframe n (n=1, 2, through apartial band (for example, through a partial band in the frequency axisof subframe n+2). In this case, the difference between a time point atwhich an aperiodic SRS triggering grant is received and a time point atwhich an aperiodic SRS is to be transmitted is 2 in this case. That is,when the UE is configured such that an aperiodic SRS transmissiontriggering grant is received in subframe 1 and an aperiodic SRS istransmitted in subframe 3, the UE may transmit an aperiodic SRS througha partial band 1010 of subframe 3. Similarly, when the UE is configuredsuch that an aperiodic SRS transmission triggering grant is received insubframe 5 and an aperiodic SRS is transmitted in subframe 7, the UE maytransmit an aperiodic SRS through a partial band 1020 of the subframe 7.

On the other hand, referring to FIG. 10B, according to the firstaperiodic SRS configuration, the UE may be configured such that, whenthe time relation between a subframe in which an aperiodic SRStriggering grant is received and a corresponding aperiodic SRStransmission subframe (i.e., the index difference between the subframein which the aperiodic SRS triggering grant is received and thecorresponding aperiodic SRS transmission subframe) is 1, the UEtransmits an aperiodic SRS for an aperiodic SRS triggering grantreceived in subframe n+1 (n=1, 2, . . . ) through a full band 1030 and1040 (for example, through a full band in the frequency axis of thesubframe n+2).

The term “partial-band SRS transmission” refers to transmission of anSRS using part of the band of a subframe allocated for SRS transmissionand the term “full-band SRS transmission” refers to transmission of anSRS using the entirety of the band of a subframe allocated for SRStransmission.

Full-band aperiodic SRS transmission may be selected when an uplinkchannel between the eNodeB and the UE is in a good condition. Forexample, a UE adjacent to the eNodeB or a macro UE (MUE) that is distantfrom a home eNodeB (HeNB) that uses the same transmission band as amacro eNodeB (MeNB) may perform a full-band aperiodic SRS transmissionoperation. On the other hand, partial-band aperiodic SRS transmissionmay be selected when an uplink channel between the eNodeB and the UE isin a bad condition. For example, a UE located at a cell edge or to anMUE, which is located within or near the area of a HeNB that uses thesame transmission band as an MeNB and transmits an uplink signal, mayperform a partial-band aperiodic SRS transmission operation.

The processor 255 of the UE may adaptively and flexibly switch betweenthe first and second SRS aperiodic configurations suggested in thepresent invention based on the current network state and communicationenvironments and the time point at which an aperiodic SRS triggeringgrant has been received, thereby efficiently coping with both the SRScoverage problem and the co-channel HetNet uplink signal interferenceproblem.

Especially, the second aperiodic SRS configuration shown in FIG. 10A isset based on a partial-band aperiodic SRS transmission scheme in whichaperiodic SRSs are transmitted through frequency hopping partial bands1010 and 1020. In this scheme, the UE may focus its transmission poweron part of the entire SRS resource region, thereby efficiently solvingthe SRS coverage problem.

According to the first aperiodic SRS configuration shown in FIG. 10B,when the UE is configured such that the UE transmits an aperiodic SRStransmission triggering grant in subframe 2 and transmits an aperiodicSRS in subframe 3, the UE may transmit an aperiodic SRS through a fullband 1030 of subframe 3. Similarly, when the UE is configured such thatthe UE transmits an aperiodic SRS transmission triggering grant insubframe 6 and transmits an aperiodic SRS in subframe 7, the UE maytransmit an aperiodic SRS through a full band 1040 of subframe 7.

An aperiodic SRS configuration shown in FIG. 10C may be set in anon-frequency-hopping scheme in order to solve the co-channel HetNetuplink signal interference problem although the aperiodic SRSconfiguration is set based on a partial-band aperiodic SRS transmissionscheme, similar to the second aperiodic SRS configuration. Here,orthogonal fixed partial bands 1050 and 1060 are specified as uplinksignal transmission bands for a macro UE and a home UE.

Each of the first aperiodic SRS configuration and the second aperiodicSRS configuration may be defined as one of combinations of theconfigurations of FIGS. 10A and 10B or FIGS. 10B and 10C. The eNodeB mayprovide the defined combination information and/or selected combinationinformation to the UE through higher layer signaling.

FIG. 11 illustrates an aperiodic SRS operation performed whenclassification of the index of a subframe corresponding to the timepoint at which an aperiodic SRS triggering grant arrives is appliedaccording to a different basis.

Referring to FIG. 11, let us assume that the eNodeB has allocatedsubframes 1, 3, 5, 7, and 9 as cell-specific periodic SRS subframes andhas allocated subframes 1, 5, and 9 as UE-specific periodic SRSsubframes to a specific UE. According to the aperiodic SRS configurationshown in FIG. 11, the processor 255 of the UE may select the firstaperiodic SRS configuration from among multiple SRS configurations whenthe index of a subframe in which an aperiodic SRS triggering grant hasarrived is odd (n=1, 3, 5, . . . , 9) (in the case in which the firstsubframe is indexed by 1) and may select the second aperiodic SRSconfiguration when the index of a subframe in which an aperiodic SRStriggering grant has arrived is even.

For example, if the UE receives an aperiodic SRS transmission triggeringgrant in subframe 1 which is an odd index subframe, the UE may transmitan aperiodic SRS through a full band 1110 in subframe 3 which is acell-specific aperiodic SRS subframe closest to subframe 1. In addition,if the UE receives an aperiodic SRS transmission triggering grant insubframe 6 which is an even index subframe, the UE may transmit anaperiodic SRS through a full band 1120 in subframe 7 which is acell-specific aperiodic SRS subframe closest to subframe 6.

In another embodiment of FIG. 11, when a UE-specific periodic SRSsubframe index that the eNodeB has allocated to a specific UE in aspecific frame is n (for example, n=1, 5, 9), subframes in which anaperiodic SRS triggering grant is received are divided into a subframecorresponding to a time point of n−4 and subframes corresponding to timepoints other than n−4. Here, the time point “n−4” may be variouslydefined based on other values.

In FIG. 11, if the UE receives an aperiodic SRS triggering grant in asubframe whose subframe index is 1 (i.e., a first subframe or subframe1), the UE may perform an SRS transmission operation through a full band1110 in subframe 3 which is a closest or earliest cell-specific SRSsubframe subsequent to the subframe 1 since the subframe 1 correspondsto a time point n−4 with respect to a subframe whose subframe index is 5(i.e., subframe 5). In addition, if the UE receives an aperiodic SRStriggering grant in a subframe whose subframe index is 6 (i.e., subframe6), the UE may perform an SRS transmission operation through a partialband 1120 in subframe 7 which is a cell-specific SRS subframe closest tothe subframe 6 since the subframe 6 does not correspond to a time pointn−4 with respect to a subframe whose subframe index is 9 (i.e., subframe9).

In the case where the UE has received an aperiodic SRS triggering grantin a subframe corresponding to a time point of n−4, the UE may operatein a full-band aperiodic sounding manner, i.e., according to the thirdaperiodic SRS configuration. Otherwise, the UE may operate in apartial-band aperiodic sounding manner, i.e., according to the fourthaperiodic SRS configuration. In common with the first and secondaperiodic SRS configurations, these schemes have a feature that the UEtransmits an aperiodic SRS through a cell-specific periodic SRS subframeclosest to a subframe in which an aperiodic SRS triggering grant isreceived. The third and fourth aperiodic SRS configurations may be setby the eNodeB and the eNodeB may notify the UE of the third and fourthSRS configurations through higher layer signaling.

FIGS. 12A and 12B illustrate exemplary SRS subframes of aperiodic SRSconfigurations.

Referring to FIG. 12A, the eNodeB may set a fifth aperiodic SRSconfiguration such that the UE transmits aperiodic SRSs through partialbands of subframes whose indices are 1, 5, and 9. According to the fifthaperiodic SRS configuration, the UE may transmit SRSs in subframes 1, 5,and 9 through partial bands of the subframes 1, 5, and 9 since an SRStransmission period and a subframe offset are 4 ms and 0 ms,respectively, as shown in FIG. 12A.

Referring to FIG. 12B, the eNodeB may set a sixth aperiodic SRSconfiguration such that the UE transmits aperiodic SRSs through fullbands of subframes whose indices are 3, and 7. According to the sixthaperiodic SRS configuration, the UE may transmit SRSs in subframes 3,and 7 through full bands of the subframes 3, and 7 since an SRStransmission period and a subframe offset are 4 ms and 2 ms,respectively, as shown in FIG. 12B. Here, in the fifth and sixthaperiodic SRS configurations, the period of subframes in which aperiodicSRSs are transmitted may be specified to be the same as or a multiple ofthe period of cell-specific periodic SRS subframes since resources forcell-specific periodic SRS transmission are reused as resources foraperiodic SRS transmission subframes. The eNodeB may notify the UE ofthe first and sixth aperiodic SRS configuration information (includinginformation regarding an SRS transmission subframe according to thefifth and sixth SRS configurations) through higher layer signaling.

FIG. 13 illustrates switching of aperiodic SRS configurations accordingto a time point at which a UE receives an aperiodic SRS triggering grantand the aperiodic SRS configurations of FIGS. 12A and 12B.

In the case where the UE performs aperiodic SRS transmission through acell-specific periodic SRS subframe closest to a subframe in which anaperiodic SRS triggering grant is received, the UE may perform aperiodicSRS transmission differently according to the SRS configuration of theclosest cell-specific periodic SRS subframe in which an aperiodic SRS istransmitted.

For example, as shown in FIG. 13, the cell-specific periodic SRSconfiguration is set such that subframes 1, 3, 5, 7, and 9 are allocatedas periodic SRS transmission subframes. The eNodeB may allocatesubframes 1, 5, and 9 as UE-specific periodic SRS transmissionsubframes. When the UE has received an aperiodic SRS triggering grant insubframe 1, the UE may transmit an aperiodic SRS through subframe 3which is a cell-specific periodic SRS subframe closest to the subframe1. Here, since cell-specific aperiodic SRS subframe 3 which is closestto the time point at which an aperiodic SRS triggering grant is receivedcorresponds to a subframe which is configured according to the sixthaperiodic SRS configuration in FIG. 12B, the UE may transmit anaperiodic SRS through a full band 1310 of the subframe 3. In anotherembodiment, the UE may transmit an aperiodic SRS through a full band1310 of the subframe 3 since the subframe 1, in which the UE hasreceived the aperiodic SRS triggering grant, corresponds to a time pointof n−4 with respect to the subframe 5 which is a cell-specific periodicSRS subframe, similar to the third SRS configuration.

In addition, when the UE has received an aperiodic SRS triggering grantin subframe 8, the UE may transmit an aperiodic SRS through subframe 9which is a cell-specific periodic SRS subframe closest to the subframe8. Here, since cell-specific aperiodic SRS subframe 9 which is closestto the time point at which an aperiodic SRS triggering grant is receivedis a subframe which is configured according to the fifth aperiodic SRSconfiguration shown in FIG. 12A, the UE may transmit an aperiodic SRSthrough a partial band 1320 of the subframe 9. In another embodiment,the UE may transmit an aperiodic SRS through a partial band 1320 of thesubframe 3 since the subframe 8, in which the UE has received theaperiodic SRS triggering grant, does not correspond to a time point ofn−4 with respect to the subframe 9 which is a cell-specific periodic SRSsubframe, similar to the fourth SRS configuration.

The subframe 9 is allocated as a UE-specific periodic SRS subframe suchthat the subframe 9 is basically used to perform periodic SRStransmission. However, exceptionally, the UE may cancel periodic SRStransmission and transmit an aperiodic SRS when the subframe 9 overlapsan aperiodic SRS transmission time point.

FIGS. 14A and 14B illustrate fallback aperiodic SRS transmission.

A seventh aperiodic SRS configuration and an eighth aperiodic SRSconfiguration shown respectively in FIGS. 14A and 14B are set such thatthe UE transmits an aperiodic SRS through a full band or a partial bandusing the time difference between a time point (for example, a subframeindex) at which an aperiodic sRS transmission triggering grant has beenreceived and a time point at which an aperiodic SRS transmission time isto be transmitted.

The eNodeB may allocate SRS subframes according to a seventh aperiodicSRS configuration as shown in FIG. 14A. The seventh aperiodic SRSconfiguration is set such that aperiodic SRSs are transmitted throughfull bands similar to the aperiodic SRS triggering scheme (i.e., thefirst SRS configuration scheme) shown in FIG. 10B. However, in theseventh aperiodic SRS configuration, a conventional aperiodic SRSresource, which is used through a full band thereof, is divided into areconfigured full-band aperiodic SRS resource 1410 and a fallbackaperiodic SRS resource 1415.

As shown in FIG. 14A, a partial reduced resource block (RB) region 1415of the allocated full-band aperiodic SRS resource 1410 may be used asthe fallback aperiodic SRS resource 1415. Alternatively, the aperiodicSRS resource 1415 may be predefined as a resource region disjointed fromthe full-band aperiodic SRS resource.

The scheme expressed by “fallback aperiodic SRS resource” in FIGS. 14Aand 14B indicates both the fallback aperiodic SRS resource allocationschemes described above (i.e., the “reconfigured full-band aperiodic SRSresource” scheme and the “fallback aperiodic SRS resource” scheme)rather than one of the two fallback aperiodic SRS resource allocationschemes. In addition, the fallback aperiodic SRS resource 1415 mayoccupy a resource region smaller than the reconfigured full-bandaperiodic SRS resource 1410 and the fallback aperiodic SRS resources1415 and 1425 may be allocated in a frequency hopping pattern for eachSRS transmission subframe.

The UE performs switching between the reconfigured full-band aperiodicSRS resource and the fallback aperiodic SRS resource in the followingmanner. The processor 255 of the UE compares the currently availableamount of power with the amount of power required to successfullytransmit an aperiodic SRS through the reconfigured full-band aperiodicSRS resource 1410. The processor 255 transmits an SRS through thereconfigured full-band aperiodic SRS resource 1410 when the currentlyavailable amount of power is sufficient and falls back to the fallbackaperiodic SRS resource 1415 and transmits an SRS through the fallbackaperiodic SRS resource 1415 when the currently available amount of poweris insufficient. Here, since switching to the fallback aperiodic SRSresource 1415 is performed according to determination of the processor255 of the UE, the eNodeB needs to find a resource region, in which anaperiodic SRS has been transmitted, through blind decoding.

The processor 255 of the UE may determine whether or not transmissionpower is sufficient and then may transmit an SRS through a reconfiguredfull-band aperiodic SRS resource 1410 in subframe 3 upon determiningthat transmission power is sufficient. In addition, the UE may receivean aperiodic SRS triggering grant in subframe 6 and, when the processor255 of the UE determines that transmission power is insufficient, the UEmay switch the SRS transmission scheme to the fallback aperiodic SRStransmission scheme in subframe 7 to transmit an aperiodic SRS through afallback aperiodic SRS resource 1415. This operation may also be appliedto a partial-band aperiodic sounding scheme.

The eNodeB may configure SRS subframes as shown in FIG. 14B according toan eighth aperiodic SRS configuration. The eighth aperiodic SRSconfiguration is an aperiodic SRS transmission scheme in which apartial-band aperiodic SRS resource is divided into a reconfiguredpartial-band aperiodic SRS resource 1430 and a fallback aperiodic SRSresource 1440 as shown in FIG. 14B. Here, the aperiodic SRS triggeringmethod follows the same scheme as the scheme (i.e., the second SRSconfiguration scheme) used in FIG. 10A and the fallback aperiodic SRSresource 1440 may be predefined as a resource region disjointed from thepartial band aperiodic SRS resource 1430 as shown in FIG. 14B. A partialreduced resource block (RB) region of the allocated partial-bandaperiodic SRS resource may also be used as the fallback aperiodic SRSresource 1440.

As shown in FIG. 14B, the UE may receive an aperiodic SRS triggeringgrant in subframe 1 and the processor 255 of the UE may determinewhether or not transmission power is sufficient. Then, upon determiningthat transmission power is sufficient, the UE may sufficiently performSRS transmission through a partial-band aperiodic SRS resource 1430using the transmission power. In addition, the UE may receive anaperiodic SRS triggering grant in subframe 5 and, when the processor 255of the UE determines that transmission power is insufficient, the UE mayswitch the SRS transmission scheme to the fallback aperiodic SRStransmission scheme and transmit an aperiodic SRS through a fallbackaperiodic SRS resource 1450 of subframe 7. In this case, the UE mayperform aperiodic SRS transmission through a fallback aperiodic SRSresource 1450. Accordingly, the UE can adaptively fall back to analternative aperiodic SRS resource to efficiently solve the SRS coverageproblem. Then, when the UE transmits an aperiodic SRS through a fallbackaperiodic SRS resource, the eNodeB needs to search for a resourceregion, in which an aperiodic SRS has been transmitted, through blinddecoding. In the above example, the processor 255 of the UE determineswhether or not to switch fallback aperiodic SRS schemes by determiningwhether or not power is sufficient. However, the UE may also operateaccording to a fallback aperiodic SRS scheme for a specific band uponreceiving adjacent cell interference notification information such asinformation indicating that the serving cell receives, from an adjacentcell, strong interference in the specific band. For example, if uplinkSRS transmission causes strong interference to cell B when UE A locatedat an edge of adjacent cell A transmits an SRS in a specific band ofsubframe 1, cell B may provide signaling (for example, 1-bit signaling)such as information instructing a UE in cell B to transmit an aperiodicSRS through a fallback aperiodic SRS resource taking into uplinkinterference. Then, the UE in cell B may transmit an SRS through afallback aperiodic SRS resource in subframe 1 based on such signaling.Cell A and cell B may exchange information regarding such uplinkinterference through a backhaul or the like and allocate SRS resourcesof the UE in the cell taking into consideration uplink interferenceaccording to SRS transmission of the adjacent cell.

FIG. 15A illustrates a cell-specific SRS subframe configuration and acell-specific SRS resource configuration, FIG. 15B illustrates an SRSconfiguration in which a cell-specific periodic SRS resource and acell-specific aperiodic SRS resource are multiplexed, and FIG. 15Cillustrates an exemplary aperiodic SRS subframe configuration.

Referring to FIG. 15A, the eNodeB may configure subframes 1, 3, 5, 7,and 9 as cell-specific SRS subframes at intervals of 2 ms according to apreset rule and allocate cell-specific SRS resources accordingly. The UEmay transmit an aperiodic SRS through an aperiodic SRS subframe or asubframe in which a cell-specific periodic SRS resource and acell-specific aperiodic SRS resource are multiplexed.

Referring to FIGS. 15B and 15C, from among the cell-specific SRSsubframes configured in FIG. 15A, the eNodeB may separately configuresubframes such as subframes 1, 5, and 9 in which cell-specific periodicand aperiodic SRS resources are multiplexed and ‘periodic SRS subframes’such as subframes 3 and 7. Here, in this scheme, the subframes in whichcell-specific periodic and aperiodic SRS resources are multiplexed areused while the cell-specific SRS resources are divided into a ‘periodicSRS resource’ 1510 and an ‘aperiodic SRS resource’ 1520.

In one cell-specific SRS resource division method, a cell-specific SRSresource is divided into two orthogonal regions (for example, 2subbands). In an alternative method, an entire set including pairs (orsets) of available combs and cyclic shifts may be divided into twosubsets and a periodic SRS resource and an aperiodic SRS resource may beallocated respectively to the two subsets. In the latter method, forexample, two available combs may be divided into a comb for full-bandsounding and a comb for partial-band sounding and then 8 cyclic shiftsthat can be combined with each comb may be divided into two halves, eachincluding 4 cyclic shifts, and the two halves may then be allocated as aperiodic SRS resource and an aperiodic SRS resource, respectively.

For example, UE A may transmit an aperiodic SRS through an aperiodic SRSresource 1520 in subframe 1 while UE B transmits a periodic SRS througha periodic SRS resource 1510 in subframe 1. That is, the aperiodic SRSof the UE A and the periodic SRS of UE B may be multiplexed andtransmitted in subframe 1. Here, one UE may multiplex and transmit anaperiodic SRS and a periodic SRS in subframe 1 by applying differentcombs to a periodic SRS and an aperiodic SRS, thereby increasing theefficiency of channel estimation of a specific bandwidth.

Referring to FIG. 15C, in subframes 3 and 7 among the cell-specific SRSsubframes configured in FIG. 15A, the eNodeB may allocate resources foraperiodic SRS transmission through a full band 1530.

As shown in FIGS. 15B and 15C, the eNodeB may alternately allocatecell-specific SRS subframes as a subframe in which cell-specificperiodic and aperiodic SRS resources are multiplexed and an aperiodicSRS subframe. For example, the eNodeB may configure cell-specific SRSsubframes such that cell-specific periodic and aperiodic SRS resourcesare multiplexed in cell-specific SRS subframe 1, subsequentcell-specific SRS subframe 3 is used as an aperiodic SRS subframe, andcell-specific periodic and aperiodic SRS resources are multiplexed insubsequent cell-specific SRS subframe 5 (ninth aperiodic SRSconfiguration). A rule used in this case may be defined variously usinga number of methods. In the example of FIG. 15B, a cell-specific SRSresource is not necessarily divided into periodic and aperiodic SRSresources using one of the two cell-specific SRS resource divisionmethods and a cell-specific SRS resource may also be divided intoperiodic and aperiodic SRS resources using both the SRS resourcedivision methods.

In addition, when aperiodic SRS transmission in a subframe in whichcell-specific periodic and aperiodic SRS resources are multiplexed hasbeen requested, the UE may transmit SRSs through a specified aperiodicSRS resource. The eNodeB may predefined and allocate resources foraperiodic SRS transmission of UEs since each UE does not know when anaperiodic SRS triggering indicator (for example, a grant) is received.Each subframe in which cell-specific periodic and aperiodic SRSresources are multiplexed has been basically configured such thatperiodic SRS transmission is performed in the subframe. However,exceptionally, the UE may cancel periodic SRS transmission andpreferentially perform aperiodic SRS transmission when the subframeoverlaps an aperiodic SRS transmission time point.

FIG. 16 illustrates a configuration of a UE-specific periodic SRSsubframe.

The eNodeB may allocate an SRS transmission subframe to a specific UE asshown in FIG. 16 according to a 10th SRS configuration. In the 10th SRSconfiguration, UE-specific periodic SRS subframes are allocated atintervals of 2 ms in a specific frame. For example, subframes 1, 3, 5 7,and 9 are allocated as UE-specific periodic SRS subframes in a specificframe. Some subframes among UE-specific periodic SRS subframes may beconfigured as subframes in which cell-specific periodic and aperiodicSRS resources are multiplexed as denoted by dashed lines in FIG. 16.Although cell-specific periodic and aperiodic SRS resources in subframesdenoted by dashed lines in FIG. 16 are illustrated as being multiplexedaccording to a Frequency Division Multiplexing (FDM) scheme, themultiplexing method is not limited to FDM. Cell-specific periodic andaperiodic SRSs may be multiplexed and transmitted in subframes 1, 5, and9. For example, in subframes 1, 5, and 9, the UE A may transmit acell-common periodic SRS and the UE B may transmit a periodic SRS.Alternatively, in subframes 1, 5, and 9, the UE A may multiplex anaperiodic SRS and a periodic SRS in one subframe to simultaneouslytransmit the aperiodic SRS and the periodic SRS in the subframe. Theperiod of periodic SRS subframes that are allocated in a cell-specificmanner may be set to be the same as or a multiple of the period ofcell-specific periodic and aperiodic SRS multiplexed subframes.

FIGS. 17A to 17(c) illustrate an operation for dynamically selectingmultiple SRS configurations using a time relationship between a subframein which an aperiodic SRS triggering grant is received and a subframe inwhich a corresponding aperiodic SRS is transmitted.

Here, the UE has two types of aperiodic SRS configurations which arereferred to as an 11th SRS configuration and a 12th SRS configuration.In addition, let us assume that a time point at which the UE transmitsan aperiodic SRS is specified to be a closest (or earliest)cell-specific SRS subframe subsequent to a subframe in which anaperiodic SRS triggering grant is received and the period ofcell-specific SRS subframes is set to 2 ms.

The eNodeB may allocate SRS subframes as shown in FIG. 17A according tothe 11th SRS configuration. In the case where the UE has received anaperiodic SRS triggering grant in subframe n (for example, n=5, 9), theprocessor 255 of the UE may select the 11th SRS configuration and the UEmay transmit aperiodic SRSs in subframe n+2 (i.e., n+2=7, 1) throughpartial bands 1710 and 1720 according to the 11th SRS configuration. Inthe 11th SRS configuration, the partial bands 1710 and 1720 throughwhich the UE transmits aperiodic SRSs are configured in a frequencyhopping manner.

The eNodeB may allocate SRS subframes as shown in FIG. 17B according tothe 12th SRS configuration. In the case where the UE has received anaperiodic SRS triggering grant in subframe n (for example, n=2, 8) thatis not allocated as a periodic SRS subframe, the processor 255 of the UEmay select the 12th SRS configuration and the UE may transmit aperiodicSRSs in subframe n+1 (i.e., n+1=3, 9) through a full band thereofaccording to the 12th SRS configuration.

Here, for example, let us assume that one frame includes 10 subframesand subframe indices 1 to 10 are assigned respectively to the 10subframes included in one frame. When the difference between the indexof a subframe in which an aperiodic SRS triggering grant has beenreceived and the index of a subframe in which an aperiodic SRStriggering grant is to be transmitted (which corresponds to a timerelationship between a subframe in which an aperiodic SRS triggeringgrant has been received and a subframe in which an aperiodic SRStriggering grant is to be transmitted) is 2, the processor 255 of the UEmay select the 11th SRS configuration, for example, if the UE hasreceived the aperiodic SRS triggering grant in subframe 5 as shown inFIG. 17A, and may perform an aperiodic SRS transmission operationthrough a partial band 1710 in subframe 7 according to the 11th SRSconfiguration. On the other hand, when the difference between the indexof a subframe in which an aperiodic SRS triggering grant has beenreceived and the index of a subframe in which an aperiodic SRStriggering grant is to be transmitted (which corresponds to a timerelationship between a subframe in which an aperiodic SRS triggeringgrant has been received and a subframe in which an aperiodic SRStriggering grant is to be transmitted) is 1, the processor 255 of the UEmay select the 12th SRS configuration, for example, if the UE hasreceived the aperiodic SRS triggering grant in subframe as shown in FIG.17B, and may perform a full band aperiodic SRS transmission operation insubframe 9 according to the 12th SRS configuration. Although a resourceused to transmit an aperiodic SRS in subframe 9 is denoted by a dashedline 1740 in FIG. 17B, the aperiodic SRS is actually transmitted througha full band. That is, an aperiodic SRS may be discriminated from aperiodic SRS through a comb, a cyclic shift, or the like and theaperiodic SRS may be transmitted together with the comb, the cyclicshift, or the like through a full band.

When full-band or partial-band aperiodic SRS transmission has beenrequested in a subframe in which cell-specific periodic and aperiodicSRSs are multiplexed, the UE may perform SRS transmission according tothe first aperiodic SRS configuration or SRS transmission according tothe second aperiodic SRS configuration through a specified aperiodic SRSresource.

As shown in FIG. 17A, partial-band aperiodic SRS resources may beallocated in a frequency hopping pattern (as denoted by “1710” and“1720”) to efficiently overcome the SRS coverage problem throughdiversity gain or the like.

The eNodeB may allocate SRS subframes as shown in FIG. 17(c) accordingto a 13th SRS configuration. The 13th SRS configuration, which is anexemplary partial-band aperiodic SRS configuration, is based on apartial-band aperiodic SRS scheme which does not use frequency hopping.Partial-band aperiodic SRS transmission, which does not use a frequencyhopping scheme, is included in the 13th SRS configuration. When the UEhas received an aperiodic SRS triggering grant in subframe 5, the UE maytransmit an aperiodic SRS through a partial band 1750 of subframe 7which is an earliest subframe subsequent to the subframe 5. In addition,when the UE has received an aperiodic SRS triggering grant in subframe9, the UE may transmit an aperiodic SRS through a partial band 1760 ofsubframe 1 in a frame subsequent to the subframe 9. The partial-bandaperiodic SRS transmission scheme which does not use frequency hoppingis significantly effective in alleviating the uplink signal interferenceproblem caused by use of a co-channel between HetNets.

FIG. 18 illustrates aperiodic SRS transmission performed whenclassification of the index of a subframe corresponding to the timepoint at which an aperiodic SRS triggering grant is received is appliedaccording to a different basis.

In FIG. 18, when the index of a subframe in which the UE has received anaperiodic SRS triggering indicator (grant) is odd (for example, when theaperiodic SRS triggering grant is received in subframe 1 as shown inFIG. 18), the UE may perform an aperiodic SRS transmission operationthrough a full band in subframe 3. On the other hand, when the index ofa subframe in which the UE has received an aperiodic SRS triggeringgrant is even (for example, when the aperiodic SRS triggering grant isreceived in subframe 6 as shown in FIG. 18), the UE may perform apartial-band aperiodic SRS transmission operation in subframe 7.

In another embodiment associated with FIG. 18, when a UE-specificperiodic SRS subframe index allocated to a specific UE is n, subframesin which the UE has received an aperiodic SRS triggering grant aredivided into a subframe corresponding to a time point of index n−4 andother subframes. Here, the time point of subframe n−4 whose index is“n−4” may be variously defined based on other values.

When the UE has received an aperiodic SRS triggering grant at a timepoint of subframe n−4, the UE may transmit an aperiodic SRS through afull band of a periodic SRS subframe closest to the subframe n. On theother hand, when the UE has received an aperiodic SRS triggering grantin a subframe corresponding to a time point different from that of thesubframe n−4, the UE may transmit an aperiodic SRS through a partialband of a periodic SRS subframe closest to the subframe n. Both the SRSconfigurations employ a scheme in which the UE performs aperiodic SRStransmission through a periodic SRS subframe closest to a subframe inwhich the UE has received an aperiodic SRS triggering grant.

As shown in FIG. 18, for example, in the case where the UE has receivedan aperiodic SRS triggering grant in subframe 1, the UE may perform anoperation for transmitting an aperiodic SRS through a full band 1810since the subframe 1 corresponds to a time point of n−4 with respect tothe subframe 5 (n=5). On the other hand, in the case where the UE hasreceived an aperiodic SRS triggering grant in subframe 6, the UEperforms an operation for transmitting an aperiodic SRS through apartial band 1820 since the subframe 6 does not correspond to a subframeof time point n−4 with respect to the subframe 9 (n=9).

FIGS. 19A and 19B illustrate exemplary aperiodic SRS subframes of SRSconfigurations.

For ease of explanation, only up to a second frame is illustrated inFIGS. 19A and 19B although frames subsequent to the second frame arealso present. As shown in FIG. 19A, an SRS configuration fortransmitting an SRS through a partial band may be set so as to have anSRS transmission period (or interval) of 4 ms and a subframe offset of 2ms. The eNodeB may configure subframes 3 and 7 of a first frame andsubframes 1 and 5 of a second frame as SRS subframes through a partialband. That is, the UE may transmit SRSs through partial bands insubframes 3 and 7 in the first frame and in subframes 1 and 5 in thesecond frame subsequent to the first frame. As shown in FIG. 19B, an SRSconfiguration for transmitting an SRS through a full band may be set soas to have an SRS transmission period of 4 ms and a subframe offset of 0ms. The eNodeB may configure subframes 1, 5, and 9 of a first frame andsubframe 3 of a second frame as SRS subframes through a full band. Thatis, the UE may transmit SRSs through full bands in subframes 1, 5, and 9in the first frame and in subframe 3 in the second frame subsequent tothe first frame.

In each of the SRS configurations, the period of subframes in whichaperiodic SRSs are transmitted may be specified to be the same as or amultiple of the period of cell-specific periodic SRS subframes sinceresources for cell-specific periodic SRS transmission are reused asresources for SRS transmission subframes. Although information regardingeach subframe for transmitting an SRS through a partial band and eachsubframe for transmitting an SRS through a full band may be presetbetween the eNodeB and the UE such that the information is known to boththe eNodeB and the UE, the eNodeB may also transmit the information tothe UE through higher layer signaling or the like.

FIG. 20 illustrates switching of aperiodic SRS configuration operationsaccording to a time point at which the UE has received an aperiodic SRStriggering grant and the SRS configurations of FIGS. 19A and 19B.

The eNodeB may allocate SRS resources through a full band in subframes1, 5, and 9 while configuring the same as a subframe in which acell-specific periodic SRS resource and a cell-specific aperiodic SRSresource are multiplexed. The eNodeB may divide the SRS resources of themultiplexed subframe into 2 orthogonal regions (for example, 2 subbands)or divide a total set including pairs of available combs and cyclicshifts into 2 disjoint subsets and may then allocate the divided regionsor sections respectively as a periodic SRS resource and an aperiodic SRSresource.

In FIG. 20, it is assumed that a time point at which the UE transmits anaperiodic SRS is determined to be a cell-specific SRS subframe closestto a subframe in which an aperiodic SRS triggering grant is received. Asshown in FIG. 20, for example, when the UE has received an aperiodic SRSgrant in subframe 2, the UE may transmit an aperiodic SRS through acell-specific SRS subframe 3 which first comes after the subframe 2.Here, the UE transmits an aperiodic SRS through a partial band 2010 insubframe 3 since the subframe 3 has been set as a subframe for SRStransmission through a partial band in FIG. 19A. The UE transmits anaperiodic SRS through a full band 2010 in subframe 3. In addition, whenthe UE has received an aperiodic SRS triggering grant in subframe 8, theUE transmits an aperiodic SRS through a cell-specific SRS subframe 9closest to the subframe 8. Here, the UE transmits an aperiodic SRSthrough a full band 2020 in subframe 7 since the subframe 9 for SRStransmission has been set as a subframe for SRS transmission through afull band in FIG. 19B.

FIGS. 21A and 21B illustrate aperiodic SRS transmission according to anew scheme in which part of an aperiodic SRS transmission resource isallocated and used as a fallback aperiodic SRS transmission resource.

Here, a partial reduced resource block (RB) region of an allocatedaperiodic SRS transmission resource 2110 may be used as a fallbackaperiodic SRS resource 2115. Alternatively, an entire set includingpairs of available combs and cyclic shifts and a resource regiondisjointed from the aperiodic SRS resource may be divided into 2disjoint subsets and both may then be separately defined respectively asan aperiodic SRS resource and a fallback aperiodic SRS resource.Allocation of the fallback aperiodic SRS transmission resource shown inFIGS. 21A and 21B is not necessarily based on one of the two fallbackaperiodic SRS transmission resource allocation schemes described aboveand may also be based on both the two schemes.

The partial-band aperiodic SRS transmission scheme shown in FIG. 21A isan aperiodic SRS triggering scheme in which partial-band aperiodic SRStransmission is performed, similar to the scheme of FIG. 20. When the UEhas received an aperiodic SRS triggering grant in subframe 2, the UE maytransmit an aperiodic SRS through a partial band 2110 of subframe 3which is a cell-specific periodic SRS subframe closest to subframe 2.When the UE has received an aperiodic SRS triggering grant in subframe6, the UE may transmit an aperiodic SRS in subframe 7 which is acell-specific periodic SRS subframe closest to the subframe 6. Here, theprocessor 255 of the UE may switch SRS transmission to SRS transmissionthrough a fallback aperiodic SRS transmission resource 2120 due toinsufficient transmission power or the like in subframe 7.

The full-band aperiodic SRS transmission scheme shown in FIG. 21B is anaperiodic SRS triggering scheme in which full-band aperiodic SRStransmission is performed, similar to the scheme of FIG. 20. Accordingto the full-band aperiodic SRS transmission scheme shown in FIG. 21B,when the UE has received an aperiodic SRS triggering grant in subframe3, the UE may transmit an aperiodic SRS in subframe 5 which is acell-specific periodic SRS subframe closest to the subframe 3. Here, theUE may transmit an aperiodic SRS through a fallback aperiodic SRSresource 2130 in subframe 5. In addition, when the UE has received anaperiodic SRS triggering grant in subframe 8, the UE may transmit an SRSthrough a full band 2140 in subframe 9 which corresponds to acell-specific periodic SRS transmission subframe closest to the subframe8.

The eNodeB may notify the UE of such SRS configuration information ofFIGS. 21A and 21B through higher layer signaling.

Methods for a UE to transmit aperiodic SRSs in a system next to 3GPP LTERelease 10 have been described above. The purpose of introducing anaperiodic SRS in the 3GPP LTE Release 10 system is to improve thequality of channel estimation by the eNodeB and to more accurately andadaptively estimate channels while reducing overhead of periodic SRStransmission.

The present invention suggests, as another embodiment, a new scheme inwhich aperiodic SRS transmission control is performed using a differentmethod from when periodic SRS transmission control is performed in orderto increase accuracy and efficiency of results of channel estimation ofan eNodeB obtained through aperiodic SRS transmission from a UE whenaperiodic SRS transmission is performed using various SRS triggeringschemes. The scheme suggested in the present invention may be applied tovarious aperiodic SRS duration environments.

A conventional SRS transmission power equation may be expressed as thefollowing Equation 16.

$\begin{matrix}{{P_{SRS}(i)} = {\min{\left\{ {P_{CMAX},{P_{{SRS}\;\_\;{OFFSET}} + {10\mspace{14mu}{\log_{10}\left( M_{SRS} \right)}} + {P_{O\;\_\;{PUSCH}}(j)} + {{\alpha(j)} \cdot {PL}} + {f(i)}}} \right\}\lbrack{dBm}\rbrack}}} & \left\lbrack {{Equation}\mspace{14mu} 16} \right\rbrack\end{matrix}$

Here, i denotes a subframe index and P_(SRS)(i) denotes power of an SRStransmitted in subframe i (subframe of index i). Equation 16 includesparameters that the eNodeB semi-statically determines and signals to theUE through higher layer signaling and parameters that the eNodeBdynamically determines and signals to the UE through a Transmit PowerControl (TPC) command of a PDCCH.

The eNodeB notifies the UE of P_(SRS) _(_) _(OFFSET), M_(SRS), P_(O)_(_) _(PUSCH(j)), and α(j) through a higher layer signal and dynamicallynotifies the UE of f(i) through a TPC command of a PDCCH. The eNodeBsignals P_(SRS) _(_) _(OFFSET), which is a UE-specific parameter of, forexample, 4 bits indicating a power offset value for SRS transmission, tothe UE as a semi-statically configured value in a higher layer. f(i) isa value indicating a current PUSCH power control adjustment state andcan be represented as a current absolute value or an accumulated value.α(j) is a cell-specific parameter that the eNodeB transmits, forexample, as a 3-bit value in a higher layer. αε{0, 0.4, 0.5, 0.6, 0.7,0.8, 0.9, 1} when j=0 or 1 and α(j)=1 when j=2. α(j) is a value that theeNodeB signals to the UE.

P_(CMAX) denotes configured UE transmission power, M_(SRS) denotes abandwidth of SRS transmission in subframe i expressed as a number ofresource blocks, and P_(O) _(_) _(PUSCH)(j), which the eNodeB signals tothe UE, is a parameter configured as the sum of a cell-specific nominalcomponent provided from the higher layer and a UE-specific componentP_(O) _(_) _(UE) _(_) _(PUSCH)(j) provided from in the higher layer.α(j) is a cell-specific parameter that the eNodeB transmits as a 3-bitvalue in the higher layer.

PL is a downlink path loss (or signal loss) estimation calculated in dBand is expressed as PL=referenceSignalPower−higher layer filteredRSRP.

Equations for different transmission power control of a period SRS andan aperiodic SRS may be defined by redefining the configured parametersof Equation 16 or adding new parameters to Equation 16.

A power control equation for SRS transmission suggested in the presentinvention may be represented by the following Equation 17.

$\begin{matrix}{{{P_{SRS}(i)} = {\min{\left\{ {P_{CMAX},{P_{{SRS}\;\_\;{OFFSET}} + {10\mspace{14mu}{\log_{10}\left( M_{SRS} \right)}} + {P_{O_{PUSCH}}(j)} + {{\alpha(j)} \cdot {PL}} + {H(i)}}} \right\}\lbrack{dBm}\rbrack}}}\mspace{20mu}{{H(i)} = \left\{ \begin{matrix}{{f(i)},} & {{if}\mspace{14mu}{periodic}\mspace{14mu}{SRS}\mspace{14mu}{transmission}} \\{{{f(i)} + V},} & {{if}\mspace{14mu}{Aperiodic}\mspace{14mu}{SRS}\mspace{14mu}{transmission}}\end{matrix} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 17} \right\rbrack\end{matrix}$

Here, V represents a power offset applied only for aperiodic SRStransmission. The eNodeB may signal V to the UE as one or a plurality ofvalues through a higher layer signal. When V has been set as a singlevalue, the same aperiodic SRS power offset may always be appliedregardless of the type of an accumulation-enabled value which is aUE-specific parameter and the DCI format (0/3/3A). On the other hand,when V has been set as a plurality of values, a different aperiodicpower offset may be applied depending on a combination of theaccumulation-enabled value and the DCI format (0/3/3A). For example, apower offset applied after a TPC command of a PDCCH is received may beset differently depending on the type of an SRS that the UE transmits insubframe i. Here, the values of P_(SRS) _(_) _(OFFSET), M_(SRS), P_(O)_(_) _(PUSCH(j)), α(j), PL, and f(i) are commonly applied to periodicand aperiodic SRSs while different values of V are applied to periodicand aperiodic SRSs.

Different power control equations for SRS transmission suggested in thepresent invention may be expressed as the following Equation 18. Inthese power control equations, transmission power offsets for periodicand aperiodic SRSs are calculated completely independent of each other.That is, H(i) of Equation 17 may be redefined as in the followingEquation 18. In this operation scheme, P_(SRS) _(_) _(OFFSET), M_(SRS),P_(O) _(_) _(PUSCH(j)), α(j), and PL values are shared between periodicand aperiodic SRSs while different values of f(i) are applied toperiodic and aperiodic SRSs.

$\begin{matrix}{{{P_{SRS}(i)} = {\min{\left\{ {P_{CMAX},{P_{{SRS}\;\_\;{OFFSET}} + {10\mspace{14mu}{\log_{10}\left( M_{SRS} \right)}} + {P_{O_{PUSCH}}(j)} + {{\alpha(j)} \cdot {PL}} + {H(i)}}} \right\}\lbrack{dBm}\rbrack}}}\mspace{20mu}{{H(i)} = \left\{ \begin{matrix}{{f(i)},} & {{if}\mspace{14mu}{periodic}\mspace{14mu}{SRS}\mspace{14mu}{transmission}} \\{{A(i)},} & {{if}\mspace{14mu}{aperiodic}\mspace{14mu}{SRS}\mspace{14mu}{transmission}}\end{matrix} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 18} \right\rbrack\end{matrix}$

Here, A(i) is based on the same calculation scheme as f(i) whileδ_(PUSCH), which is selected according to a combination of DCI format(0/3/3A) and accumulation-enabled values, may be set differently fromf(i). A(i) may also be defined using a calculation scheme and aδ_(PUSCH) which are completely different from f(i).

In addition, as expressed in Equation 18, the f(i) value in the powercontrol equation for periodic SRS transmission and the f(i) value in thepower control equation for aperiodic SRS transmission are not common butare independent. As an embodiment in which f(i) is independently appliedto periodic SRS transmission and aperiodic SRS transmission in thismanner, the present invention suggests a method using TPC information ofa DCI format transmitted for SRS triggering. The eNodeB may use, as aDCI format for aperiodic SRS triggering, a conventional DCI formatincluding an aperiodic SRS triggering bit or a DCI format newly definedonly for aperiodic SRS triggering. In addition, let us assume that a DCIformat for aperiodic SRS triggering always has 2-bit TPC information. Inthe suggested method, the eNodeB directly and dynamically signals apower offset value to the UE through 2-bit TPC information under such acondition. The power offset may be an absolute or accumulated value.This power offset affects only aperiodic SRS transmission power control.

Another power control equation for SRS transmission suggested in thepresent invention may be expressed as the following Equation.

$\begin{matrix}{{{P_{SRS}(i)} = {\min{\left\{ {P_{CMAX},{P_{{SRS}\;\_\;{OFFSET}} + {10\mspace{14mu}{\log_{10}\left( M_{SRS} \right)}} + {P_{O\;\_\;{PUSCH}}(j)} + {{\alpha(j)} \cdot {PL}} + {f(i)}}} \right\}\lbrack{dBm}\rbrack}}}{P_{{SRS}\;\_\;{OFFSET}} = \left\{ \begin{matrix}{P_{{Apeiodic}\;\_\;{SRS}\;\_\;{OFFSET}},} & {{if}\mspace{14mu}{aperiodic}\mspace{14mu}{SRS}\mspace{14mu}{transmission}} \\{P_{{Periodic}\mspace{20mu}{SRS}\mspace{20mu}{OFFSET}},} & {{if}\mspace{14mu}{Periodic}\mspace{14mu}{SRS}\mspace{14mu}{transmission}}\end{matrix} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 19} \right\rbrack\end{matrix}$

In this scheme, the eNodeB signals two UE-specific PSRS_OFF_(SET) valuesrather than one UE-specific P_(SRS) _(_) _(OFFSET) value through ahigher layer signal so as to apply different power offsets for SRStypes. The eNodeB may discriminate between periodic SRS transmission andaperiodic SRS transmission so as to signal respective P_(SRS) _(_)_(OFFSET) values of periodic SRS transmission and aperiodic SRStransmission to the UE. For example, in trigger type 0, the eNodeB maynotify the UE of a power offset value for periodic SRS transmissionthrough higher layer signaling. In addition, in trigger type 1, theeNodeB may notify the UE of a power offset value for aperiodic SRStransmission through higher layer signaling. Here, the eNodeB maytransmit a power offset value for aperiodic SRS transmission to the UEthrough DCI format 0/4/1A in the FDD and TDD systems or may transmit apower offset value for aperiodic SRS transmission to the UE through DCIformat 2B/2C in the TDD system. When triggering of trigger type 0 andtriggering of trigger type 1 are simultaneously performed (orsimultaneously occur), the UE may perform only trigger type 1 SRStransmission (i.e., aperiodic SRS transmission).

In this case, all parameters excluding P_(SRS) _(_) _(OFFSET) are commonto a power control equation for periodic SRS transmission and a powercontrol equation for aperiodic SRS transmission. The same operation maybe performed using P_(O) _(_) _(PUSCH) instead of P_(SRS) _(_)_(OFFSET). Accordingly, the processor 255 of the UE may calculate anuplink transmission power value for periodic SRS transmission and anaperiodic SRS transmission power value respectively based on a poweroffset value for periodic SRS transmission and a power offset value foraperiodic SRS transmission received from the eNodeB through higher layersignaling or the like. Another power control equation for SRStransmission suggested in the present invention may be expressed as thefollowing Equation 20.

$\begin{matrix}{{{P_{SRS}(i)} = {\min{\left\{ {P_{CMAX},{P_{{SRS}\;\_\;{OFFSET}} + {10\mspace{14mu}{\log_{10}\left( M_{SRS} \right)}} + {P_{O\;\_\;{PUSCH}}(j)} + {{\alpha(j)} \cdot {PL}} + {H(i)}}} \right\}\lbrack{dBm}\rbrack}}}{P_{{SRS}\;\_\;{OFFSET}} = \left\{ {{\begin{matrix}{P_{{Apeiodic}\;\_\;{SRS}\;\_\;{OFFSET}},} & {{if}\mspace{14mu}{aperiodic}\mspace{14mu}{SRS}\mspace{14mu}{transmission}} \\{P_{{Periodic}\mspace{20mu}{SRS}\mspace{20mu}{OFFSET}},} & {{if}\mspace{14mu}{Periodic}\mspace{14mu}{SRS}\mspace{14mu}{transmission}}\end{matrix}\mspace{20mu}{H(i)}} = \left\{ \begin{matrix}{{f(i)},} & {{if}\mspace{14mu}{periodic}\mspace{14mu}{SRS}\mspace{14mu}{transmission}} \\{{{f(i)} + V},} & {{if}\mspace{14mu}{Aperiodic}\mspace{14mu}{SRS}\mspace{14mu}{transmission}}\end{matrix} \right.} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 20} \right\rbrack\end{matrix}$

This method is a hybrid method which combines the first method describedabove with reference to Equation 17 and the third method described abovewith reference to Equation 19. In this method, the UE may set differentpowers for periodic SRS transmission and aperiodic SRS transmission. Forexample, after a power offset value for aperiodic SRS transmission isset using Equation 19, the power offset of Equation 17 is additionallyapplied to increase the selection range of offset values. In anotherembodiment, an aperiodic SRS transmission power offset set throughEquation 19 may be set as a coarse value and a power offset appliedthrough Equation 17 may be set as a relatively fine value to enable moredetailed power control than in a conventional method. The sameadvantages and results may be obtained through a combination of themethod using Equation 18 and the method using Equation 19.

The above embodiments are provided by combining components and featuresof the present invention in specific forms. The components or featuresof the present invention should be considered optional unless explicitlystated otherwise. The components or features may be implemented withoutbeing combined with other components or features. The embodiments of thepresent invention may also be provided by combining some of thecomponents and/or features. The order of the operations described abovein the embodiments of the present invention may be changed. Somecomponents or features of one embodiment may be included in anotherembodiment or may be replaced with corresponding components or featuresof another embodiment. It will be apparent that claims which are notexplicitly dependent on each other can be combined to provide anembodiment or new claims can be added through amendment after thisapplication is filed.

Those skilled in the art will appreciate that the present invention maybe embodied in other specific forms than those set forth herein withoutdeparting from the spirit and essential characteristics of the presentinvention. The above description is therefore to be construed in allaspects as illustrative and not restrictive. The scope of the inventionshould be determined by reasonable interpretation of the appended claimsand all changes coming within the equivalency range of the invention areintended to be embraced in the scope of the invention.

INDUSTRIAL APPLICABILITY

A method for transmitting, by a UE, an SRS based on aperiodic SoundingReference Signal (SRS) triggering and a method for controlling uplinktransmission power for aperiodic SRS transmission can be industriallyapplied to various wireless communication systems such as 3GPP LTE andLTE-A systems.

The invention claimed is:
 1. A method of transmitting an aperiodicsounding reference signal (SRS) by a user equipment (UE) in a wirelesscommunication system, the method comprising: receiving, by the UEthrough a higher layer signal, uplink power control information, theuplink power control information including a first power offset valuerelated to a periodic SRS transmission and a second power offset valuerelated to an aperiodic SRS transmission, the first power offset valueand the second power offset value being semi-statically configured;receiving, by the UE, information regarding plural configurations for anaperiodic SRS, wherein each configuration of the plural configurationsincludes a transmission comb value for the aperiodic SRS; receiving, bythe UE, a first downlink control information (DCI) format in a subframen, the first DCI format indicating: triggering the aperiodic SRStransmission, and a first configuration of the aperiodic SRS among fromthe plural configurations; according to the first DCI format,transmitting the aperiodic SRS based on: the second power offset; and atransmission comb value of the first configuration of the aperiodic SRS;receiving, by the UE, a second DCI format, the second DCI formatindicating: triggering the aperiodic SRS transmission; and a secondconfiguration of the aperiodic SRS among from the plural configurations;and according to the second DCI format, transmitting the aperiodic SRSbased on: the second power offset; and a transmission comb value of thesecond configuration of the aperiodic SRS, wherein the transmission combvalue of the first configuration is different from the transmission combvalue of the second configuration.
 2. The method of claim 1, wherein theuplink power control information is received through a higher layersignaling.
 3. The method of claim 2, wherein the first power offsetvalue and the second power offset value are different from each other.4. The method of claim 1, wherein the first DCI format or the second DCIformat comprises DCI format
 0. 5. A user equipment (UE) of transmittingan aperiodic sounding reference signal (SRS) in a wireless communicationsystem, the UE comprising: a transmitter; a receiver; and a processorconfigured to control: the receiver to receive uplink power controlinformation, the uplink power control information including a firstpower offset value related to a periodic SRS transmission and a secondpower offset value related to an aperiodic SRS transmission, the firstpower offset value and the second power offset value beingsemi-statically configured, and the receiver to receive, through ahigher layer signal, information regarding plural configurations for anaperiodic SRS, wherein each configuration of the plural configurationsincludes a transmission comb value for the aperiodic SRS; the receiverto receive a first downlink control information (DCI) format in asubframe n, the first DCI format indicating: triggering the aperiodicSRS transmission, and a first configuration of the aperiodic SRS amongfrom the plural configurations for the aperiodic SRS; and thetransmitter to transmit, according to the first DCI format, theaperiodic SRS based on: the second power offset; and a transmission combvalue of the indicated configuration of the aperiodic SRS, the receiverto receive, by the UE, a second DCI format, the second DCI formatindicating: triggering the aperiodic SRS transmission; and a secondconfiguration of the aperiodic SRS among from the plural configurations;and the transmitter to transmit, according to the second DCI format, theaperiodic SRS based on: the second power offset; and a transmission combvalue of the second configuration of the aperiodic SRS, wherein thetransmission comb value of the first configuration is different from thetransmission comb value of the second configuration.
 6. The UE of claim5, wherein the uplink power control information is received through ahigher layer signaling.
 7. The UE of claim 6, wherein the first poweroffset value and the second power offset value are different from eachother.
 8. The UE of claim 5, wherein the first DCI format or the secondDCI format comprises DCI format 0.